Deactivate iMessage without old SIM

I recently changed number and no longer have access to my old SIM. I have set up iMessage with my new number which is working fine. I have sent my new number to everybody and they have stored that as a new contact for me and removed my old number from their contacts. However all the old iMessage threads

still have my name associated with my old number i.e. when sending a message to me a friend will start typing in the recipient, my name comes up as an option and it is selected and the message sent. However this will often be my old number. This happens especially in group threads where there is a conversation between me, X, Y and Z. My name is listed and associated with my old number. My name (associated with my new number) is there as an option but as it lists this by name only there is no way of distinguishing my old and new number selections (unless the sender deliberately taps the ℹ at the side of my name and checks).

This is a huge problem as many, many messages are being sent to my old number and I cannot receive them. Is there any way of removing my old number from being able to receive iMessages without this SIM? Are there any other solutions?

Any help would be hugely appreciated. Thanks