My iMessage is stuck on the wrong phone number and I keep getting coded text messages from SMS Info.

Question

I recently switched the sim card in my iPhone when I moved from one country to another. When I put my local sim card in iMessage would not activate (just staying on 'waiting for activation' forever). This has not been a problem before. When I went to send/receive I saw the phone number there is still on the old one from the country I left. This is not the case in phone settings when I look for 'my phone number' or in facetime, which recognise the new number.
Plus I keep getting text messages from 'SMS Info'. They are just code, except that in there my new phone number is included among the code. The only other discernible characters are the letters 'REG-RESP?'. Perhaps this is something to do with an error in registering my new number.
I have tried-
1. Turning it off and on again.
2. Turning iMessage off and on again. This results in the usual 'it may cost you to reactivate with an SMS' popup on my phone screen, then a popup saying there has been a mistake, then one of these coded SMS messages.
3. Doing the above in combination with logging in and out of my apple id (as suggested on another forum post here)
4. Removing the new sim card and replacing the old one. Then turning off iMessage, replacing the new sim card and turning iMessage back on (of course powering the phone down and up)
None of these remedies have worked. The iMessage problem is affecting all sorts of my messages. Windows keep popping up saying that I may have to pay for an SMS to activate iMessage, except that it doesn't activate. The SMS messages from 'SMS Info' keep coming and I can't seem to get any of it to stop an just work normally.
I have looked in these forums already and can't see the same problem elsewhere. If someone could figure this out I would be most grateful.

Answer 1

Hi,
When a Mac is "registered" for iMessages account with an Apple ID the Serial Number of the Mac is used to create an Auth Token as it is called for the Messages app that allows that Mac to work.
I would guess a similar process of linking the Number of the iPhone to a Hardware fact about the device is also in place.
I would contact Apple Support and check with them.  (you might need to speak to a Level 2 person as Level 1 people are script led and try to fit everything into Software or Hardware categories where as sorting and Apple ID (which the Number is in this case) is normally Free).
I did find this iOS: Troubleshooting Messages - Apple Support
It starts off about sorting SMS that is not working.
This one has a bit on Unlinking an iPhone Number (with or without the iPhone) iOS and OS X: Link your phone number and Apple ID for use with FaceTime and iMessage - Apple Support
7:55 pm      Tuesday; January 6, 2015
​  iMac 2.5Ghz i5 2011 (Mavericks 10.9)
 G4/1GhzDual MDD (Leopard 10.5.8)
 MacBookPro 2Gb (Snow Leopard 10.6.8)
 Mac OS X (10.6.8),
 Couple of iPhones and an iPad