This can happen if Apple (for iPhone) or Google (for Android) have registered your handset with the initial number allocated to your iD account, before the number transfer took place. 

The following might help with an iPhone:

1. Turn OFF iMessage
2. Turn OFF FaceTime 
3. Turn OFF your iPhone
4. Carefully remove your SIM card and check it’s clean from smudges and not damaged
5. Insert your iD SIM card and turn ON your iPhone
6. Turn ON iMessage
7. Turn ON FaceTime

Hopefully Apple then recognise the mobile number linked with your iPhone is the number you’ve transferred to iD.
 

For Android try this:

1. Turn OFF RCS chats (“Chat features”) in the Google Messages app.
2. Turn OFF your handset and carefully remove the SIM card.
3. Check no fingerprints are visible on the SIM card, nor any damage, before re-inserting your iD SIM card.
4. Turn ON your handset.
5. Turn ON RCS chats.

Excellent!! thank you! this worked. Have a great day, and feel good about helping a noob like me 

Super @ryltarhune, are you using an iPhone or Android handset?

iphone 11

Hi @ryltarhune 

Glad to hear the suggestion above from @andewhite helped with this.

Tom

Hi, I’m also having this trouble but the above hasn’t worked for me. I feel like throwing the phone out of the window! 
 

The new iD number (that shouldn’t be on this phone) is showing up, and my old number (that I wanted and had a PAC for) isn’t coming up as an option to use for iMessage. It says the sim isn’t registered for Apple? I’m at a loss! 

Is the number you wanted to keep showing in your online iD account, @Holly Bright?

Have you checked the mobile number you wanted to keep is shown in the following locations:

• Settings > Apple ID > tYour device with the iD SIM] > Phone Number
• Settings > Phone > My Number
• Settings > Messages > Send & Receive > YOU CAN RECEIVE IMESSAGES TO AND REPLY FROM 
• Settings > Messages > Send & Receive > START NEW CONVERSATIONS FROM 
• Settings > FaceTime > YOU CAN BE REACHED BY FACETIME AT 
• Settings > FaceTime > CALLER ID

Hi, thank you for your reply. 
 

My Apple ID is my old number (the correct one), but when I go to “settings” “phone” my number is the new incorrect one and I can’t edit it? I try to and it won’t save. 

It says that my SIM card is not compatible with Apple on my Apple ID and therefore will not work for iMessage and FaceTime  

Have you tried a NETWORK RESET, @Holly Bright? 

The iOS user guide describes how to do this.

Wow, you are incredible!!!!!!! Thank you so much!!!!!!! Network reset has worked!! You absolute genius! Thank you so much! 

I’m not too sure about that, but thank you… 

Hi @Holly Bright,

Glad to hear that this is resolved.

Please get back to us if you require further assistance.

Kash

I have the same problem with iPhone 15 pro, I want to keep my old iPhone 12 number and submitted PAC and had text to say transfer to iD and transfer of number has been successful, but on settings and ‘my number’ etc as suggested above is still showing the old phone with old number as well as new phone with new unwanted number on the same apple account. I have tried resetting network settings and turning off / on iMessage/ FaceTime / phone but no change. Help!

Hey there @Trolley, we’re sorry to hear that. Is the same issue still persisting please?

Thank you,

Tyler

Hi, I have the same problem with my Samsung S24fe. I've tried all the above and done a network reset but the new number still showing on the RCS chat. 

Please help its so frustrating

​@Jo Grainger 

Have you done all of this?

(copied from)

If Google Messages doesn't show the number you're expecting please try the following steps to resolve the issue: 

1. Open Messages.
2. Tap ‘More Options’.
3. Tap ‘Settings’.
4. Tap ‘RCS chats’.
5. Turn off RCS chats.

Alternatively, use the Google Messages deactivation web portal to turn off RCS chats.

6. Restart your phone.

7. Re-enable Google Chat by following the same steps as step 1 but toggling "Chat Features" to "On".

If this doesn’t work, try clearing the cache for both Google Play Services and Google Play Store. Here’s how to do it:

1. Open ‘Settings’.

2. Tap ‘Apps’.

3. Scroll down to ‘Google Play Services’.

4. Tap ‘Google Play Services’.

5. Tap ‘Storage’.

6. Tap ‘Clear Cache’.

7. Tap ‘Manage Space’.

8. Tap ‘Clear all Data’.

9. Scroll down and tap ‘Google Play Store’.

10. Tap ‘Storage’.

11. Tap ‘Clear Cache’.

12. Tap ‘Clear data.’

If you have then (having sorted a friend of a friend of someone I don’t know the other day) we turned chat off, got them to pop to Currys to ask for a replacement SIM, activated this one and turned chat back on and it only went and blooming worked.

Yes, I've tried all of the above and still didn't work . I think I'll have to order a new sim card. Thank you 

Hi ​@Jo Grainger 

Have you tried turning RCS off for a few days and then coming back to it? I’ve seen this work for some people.

Tom

Hi Tom, I've turned RCS off and back on in a couple of minutes. I'll try to keep it off for few days thanks

Thanks ​@Jo Grainger 

Please let us know how you get on. 

Nat 

UPDATE.

I followed all the above instructions to the letter and nothing worked. 

My Samsung messages used my ported number but the Google messages used the new number .

I went to Curry's and requested a new sim card, the sale rep told me that this will not work as its a fault with Google messages but had to issue me a new sim as I insisted.

I activated the sim card through the app, 30mins later the sim was active.

Now Google messages and Samsung messages work fine with no issues.

Thank you to everybody who answered my question  

Maybe the Currys reps need to read these forums then ​@Jo Grainger 

the sale rep told me that this will not work as its a fault with Google messages but had to issue me a new sim as I insisted.

I’m so glad you insisted

(as the saying goes the customer is always right)

I did write this 3 days ago

If you have then (having sorted a friend of a friend of someone I don’t know the other day) we turned chat off, got them to pop to Currys to ask for a replacement SIM, activated this one and turned chat back on and it only went and blooming worked.

This stranger I helped could not get theirs to work and it only worked in their case by doing the above, but they weren’t told a new SIM wouldn’t fix this by the Currys they went in to.

​@Daz_S I mentioned the forum and said that I was advised on there to get a new sim, but he was determined that this will not work ‍♀️

Well I’d say that in the majority of cases, based on these very knowledgeable Currys employees and how they coming rushing towards you as soon as you enter (like baby lambs greeting a farmer), its simply the ‘youth of today’. They think they know ​@Jo Grainger 

Hi ​@Jo Grainger 

Glad to hear that’s sorted.

Tom