The phone does not ring at the certain number

It's really strange.

It this is happening calling only that specific number, I would try also to delete its related contact from your contacts, then making a test to input that number and call it (or send it a message) using the numeric keypad.

If it works, create a new contact for that number.

Pls let me know, when done.

Regards

Giulio

Sorry about that. Sorry because reading again your question I'm totally clueless.

But, as already said, if you can successfully call (or text) all other contacts, I don't see any good reason to think that your iPhone 7 (I use that same device) has something wrong or defective.

I've no further suggestions to offer you, at the moment.

Let's see if one of my colleagues (more competent than me) can help you.

Stay tuned. And if you find a solution, please keep me informed.

Thanks and regards

Giulio

It is a mystery to be sure. One possible explanation I can think of is that your IMEI number has made it onto a blacklist that the carrier for the number that you are trying to call implements, while others don't. Take a look at https://www.simsurprise.co.uk/articles/42-mobile-phones-blocked-and-blocking for some background.

tt2

Have you checked with your carrier to ensure they haven't blacklisted the number?

And in a more extreme measure, have you tried wiping the phone clean, setting up as new and trying? Just make sure you have a backup to restore from afterwards.