Sis's new iPhone 12 Pro's iMessage NOT verifying her mobile number (can't use)

Hello all,

We've been trying for days since my sis got her new iPhone 12 Pro to activate iMessage using her mobile number, but it is still verifying (spinning wheel) and at times default back the her Apple ID.

It is the same with FaceTime, no go on use via mobile number.

These are the sequence of events and what we have done so far:

1. Sis got new iPhone 12 Pro, set it up smoothly.
2. I did not, she did not, check if iMessage is using her mobile number.
3. Sis changed telco after a few days (planned) and got a new SIM card, insert new SIM, everything seems to be working, including WhatsApp.
4. I asked her if she have received any messages on the iPhone when inserting the new SIM, she said yes but couldn't recall what.
5. Checked her phone, Main Apple ID in Settings did not show her mobile number, I added in.

What we have done so far:

1. Turn off and on iMessage, no go.
2. Log out Apple ID and log back in inside iMessage, no go.
3. Turn off phone, remove SIM, re-insert, no go.
4. Reset all Network Settings, no go.

I think the only thing left we have not done is to reset the phone, reformat and re-set up again...

I am wondering at this point could the new phone and/or the SIM card be faulty?

I did noticed one thing about this phone: When shut down and turn off again, the Apple logo will flash very quickly for a moment before the logo stays lit till the Home Screen comes on.

Is this something to concern about?

I have also attached some error messages that we got:

I do not mind starting all over again, but just afraid the problem may persist.

Thank you very much!