phone number

Have you tried the following procedure, @Emma Hunt? 

1. Turn OFF RCS chats (“Chat features”) in the Google Messages app.
2. Turn OFF the handset and carefully remove the SIM card.
3. Check the SIM card is clean and undamaged, before re-inserting your iD SIM card.
4. Turn ON the handset.
5. Turn ON RCS chats. 

Hi I've tried this.  Finally got messages to send however replies  are going to my old phone, which is even worse.

Tried to disable phone number on RCS chats, sent me a code which of course isn't valid.

Sounds like Google still have your old phone linked with your mobile number, in their RCS devices database, @Emma Hunt. 

Have you tried:

1. Turn OFF RCS chats on your new phone. 
2. Remove the iD SIM card, and put it in your old phone.
3. On your old phone, turn OFF RCS chats and leave it OFF.
4. Remove the iD SIM card from your old phone. 
5. Put your iD SIM card in your new phone, and then turn ON RCS chats.

Hi @Emma Hunt 

Have you tried the above from @andewhite to turn RCS off entirely on both devices?

Tom