I have tried this but I don't have any of these options on my phone. I am using Samsung messages. Text messages send as my old number (which is what I want), chat messages send as the number the phone came with. 

First of all, try updating the number in your phone settings. To do this, just follow these simple steps:

1. Open ‘Messages’.
2. Select ‘Advanced’.
3. Select ‘Phone Number’.
4. Update the number.

If this doesn’t work, then you need to check what number is stored in your Samsung profile by following these steps:

1. Open ‘Messages’.
2. Select ‘My Profile’.
3. Select ‘Profile Sharing’.
4. Check what number is stored under ‘Registered Device’.
5. If the wrong number is stored, turn the chat off and back on again.

Still having issues? Try clearing the cache of the ‘Samsung Messages’ app. Here’s how:

1. Open ‘Settings’.
2. Tap ‘Apps’.
3. Tap ‘Samsung Messages’.
4. Tap ‘Storage’
5. Tap ‘Clear Cache’.

As a last resort, you can perform a Network Settings Reset on your phone:

1. Open ‘Settings’.
2. Tap ‘General management’.
3. Tap ‘Reset’.
4. Select ‘Reset Network Settings’.

When I open my message app I don't have any of these options. I did look at this page a couple of days ago, but I cannot follow any of these steps 

Have you tried turning off RCS messages - wait a bit and then turn it back on?

Hi ​@K_Welsh 

I’d recommend the same as ​@MZone above, it sounds like an alternative messaging service (On a Samsung, RCS) has kept your original number, we’d recommend switching it off for a few days and then back on.

Tom

Hi ​@K_Welsh 

Glad to hear that sorted it, let us know if you need any further assistance.

Tom