Sorry this number does not exist message

Hi, first time this has happened in about 15 years of owning a mobile so any help super appreciated. For some reason when I try dialling the majority of numbers on my phone I get a message saying 'sorry this number does not exist'. Doesn't happen with all of them. This just happened today.

I got a friend to dial the exact number from the same space and there's rings through no problem. My phone still receives calls and as I said happens on about 90% of numbers I've tried in my phonebook (about 15).

As I said really weird. I've tried the usual turning on and off and resetting the phone.

Thanks

Tom