Can't change Apple ID number because of country code

I forgot to change my phone number (original one is no longer usable) for my Apple ID before factory resetting my IPad. I tried to sign into it and change the number attached to it but I'm forced to use a 3 digit country code. I've went in without signing into an Apple account and the region indicated is the correct region, changing it to another one and back to the correct region doesn't work either. I've also factory reset it again (idk trying anything at this point), shutting it down and on again, but nothing.

In the end I created a new Apple account and they gave me the country code this time around, so I tried resetting my previous Apple account's phone number but still weirdly the same thing as before. Would prefer if I could access my old Apple account so any suggestions to fix this would be appreciated.