Phone number disappeared from iMessage and FaceTime

Some time ago me and my Dad changed the SIM cards in our phones (keeping the same phone number, we just changed carrier). For my sim card it worked without any problems, but for my Dad it was a little bit complicated. As his sim card was delivered with short delay - he temporarily put prepaid card in his phone to be able to contact with other people. Probably, during all this mess and making things worse, once he put the proper sim card, he accidentally taped on the option to remove the number.

Now the number is gone for good from iMessage and FaceTime. There isn’t even an option to add it back. https://i.imgur.com/zczUtNy.jpg. So I tried every fix under the sun including reinstalling the entire phone from backup. Nothing helps.

The problem became even more complicated when I noticed that when I insert any other sim in dad phone it’s instantly recognized in iMessage and FaceTime. Also, when I insert his SIM card in another phone it is instantly recognized.

The only remaining thing I can think of is to setup the phone as new, but that would leave us without the possibility of restoring from iCloud backup. Any ideas on how to fix this would be appreciated.

Things I tried:

• Turn off iMessage and Facetime and resetart phone - no success
• sign out from iMessage and Facetime and restart phone. Sign in again - no success
• Reset network settings - no success
• Remove sim card and put it back after some time - no success
• Sing out from your apple id from phone - no success
• Change apple id password - no luck
• Reset entire phone and restore it from backup - no luck