Phone number not showing in Settings

Hello everyone, I hope you're doing well.

I have been using my iPhone 11 pro for about a year and a half now and recently I've noticed that I can send iMessages only from my Apple ID. My phone number is nowhere to be found and I can't just add it under 'Phone' settings as it won't allow me to click on it - my number is just a blank space.

When I check 'Name, Phone numbers, email' in Apple ID settings both my e-mail that use for ID and my telephone number are showing but there is no way to add it under 'iMessage' or 'Facetime'. The only thing showing there is my e-mail.

I have tried logging out of Apple ID, tried turning off / on both iMessage and FT but without any success. I also tried to reset the network settings, did the factory reset and backed up the phone via iTunes, took out the sim card but nothing has helped so far.

Any ideas how to fix it?