Phone number reverted back to original SIM number?

[DrBlood]

Hi forumites

I bought a second SIM as a gift and the SIM was given and eventually the phone number change by O2 to keep the recipients mobile number. They shifted from O2 PAYG to an O2 pay monthly.

Everything was going swimmingly for a month. This week I recommended a text off said person and it's now coming from the original SIM phone number (preswitch). They still receive texts to the intended phone number but on responding come to me from the wrong number.

MyO2 States the correct phone number.

Any idea what has happened and how to resolve?

TIA

[MI5]

@DrBlood 

If an iPhone, check Settings >Phone >My Number

If Android, go to advanced message settings and edit number used for RCS services.

[DrBlood]

It's an Android (miui 12).

Tried two things with no effect.

Messaging > settings > advanced: phone number there stated unknown so populated that.

No effect.

SIM cards and mobile networks > O2 SIM

Checked the number there

No effect.

Texting worked fine until v recently. Is it possible O2 had done something whappy?

[MI5]

@DrBlood 

When you added the number in message settings did it say it was validating the number?

[DrBlood]

No it didn't

[MI5]

@DrBlood 

Check again to see if it saved the number.

When you enter a number in there, it should say validating for a few seconds whilst it handshakes with the network.

Also try rebooting the phone to see if that forces the handshake.

[DrBlood]

Sorry for the delay. The phone is my mother in law's.

So the field in Messaging > advanced settings is just like a text box. A box pops up on selecting it but what pops up is just a text box there's no loading or waiting on editing it. I tried 07... And +447... And song+44 just reverts it to 0. But no apparent handshake.

Another twist in the plot. My MiL was out with some friends and texted then both. One received it from the right number, one the wrong number... Go figure!

Told her to call O2... 

[MI5]

I think it's going to need a sim swap again but to a blank sim as the phone appears to be defaulting to the sim number.

It's now becoming an issue that O2 don't push numbers to sim cards like all the other networks do as number validation is now used more widely for apps.