When you call an old friend back, you may hear "the number you dialed was not recognized" without the phone ringing. Other operators may say that the number you have dialed cannot be reached or does not exist.
AT&T We're sorry Message
It's not common to hear this tone and usually when someone's phone is off the call goes straight to voicemail or if they can't answer it rings and then goes to voicemail so you can leave a voicemail. Since it is unusual to hear that the number you have dialed has not been recognized, it may lead you to believe that the recipient has blocked your number.
Whether you're using a landline to call this number back or you're mobile, as long as you're using a UK provider such as BT, Three, O2, EE or Virgin, you may hear "the number you dialed" has not been dialed recognized' error message when calling a number back.
It can be extremely frustrating to know that you cannot reach the number that just called you, but you will be surprised to know that in 90% of cases when you call back this number, it is actually a fake number that you call back and the number that supposedly called you is not the real caller ID, it is just a number they have used to hide their identity so that they can freely make phone calls without having to worry about anything.
