Messages disappearing from imessage

I have moved mobile phone providers, and transferred my ol number across to my new mobile phone service. Since then, when I get messages from people, it will show up in my notifications, and sometimes it will appear when I go into the messages app. When it does this, if I check a few minutes later, it has disappeared, almost like it has been filtered out. Other times it will appear, but then, as before disappear if I go and look for it again.

I can search for the missing messages, and they will show up in the search results, but when I select the message, it takes me through the conversation thread, but the message does not show.

I have tried turning off and on imessage, and facetime loads of times, I have checked and the phone number and details are correct in the settings. Messages are set to keep for forever.

Any ideas how I can fix this, I may have to just reset the phone and restore from backup, but am worried that this might just restore the fault along with the data?