Can't send a message

[Headbanger]

Hi purchased a Xiaomi Redmi note 9 Pro phone. I was on O2 PAYG so I purchased a pay monthly SIM only deal.

Wanted to keep my PAYG number and everything went fine. Setup new phone and I am unable to send messages via app or using Google assistant keep getting 'message not sent phone number formatted incorrectly'.

Searched online for help and tried various different solutions - when I setup a new phone I normally lock it down and I am careful about what I allow apps access too, but I tried allowing everything. I also edited a couple of my contacts numbers by changing number format. Made sure the phone was using the correct message centre number, to double check this out SIM card in another phone using +447802000332. Tried SIM card in another phone and it is working fine. I have another service providers SIM in the phone at the moment and it's working fine.

Any help would be much appreciated because it is driving me crazy.

Thanks

[MI5]

@Headbanger 

Have you tried clearing the message app cache?

Also check your number is correct in messaging app settings.

[Headbanger]

Yes cleared app cache, do you mean the message service number.

[MI5]

@Headbanger 

Yes, check these tips Guide: Text Message Tips (not sent or received) 

[Headbanger]

Can't actually check this number from the app so used *#*#4636#*#* and put SIM in old phone and doubled checked using message app on that phone

[Headbanger]

Have tried everything there to no avail thanks

[Headbanger]

The phone has dual SIM have tried using both. Am I right in thinking, message service number must be correct because it is able to send messages on my old phone. It also has no problems sending messages using Google assistant on old phone.

[Headbanger]

If I am able to use Xiaomi with other providers SIM then all the apps must be functioning okay. When I insert the O2 SIM card and restart phone all I do is clear cache. Then I try and send messages and same error.🤔

[MI5]

Did you get a new pay monthly sim when you changed from PAYG @Headbanger ?

[Headbanger]

Yes but I got my existing number put onto that. So I am using my new SIM. Think it might be because of the number swap, I am going to check out some of the APN settings??