Noun
A telephone number dialled by mistake, for example by transposing digits.
A telephone call received from an unfamiliar caller, due to a mistake in the number dialled. (Can we add an example for this sense?)
Who was that on the phone? It was just a wrong number.
(idiomatic, dated) An incorrect notion or understanding concerning a person or situation.
Source: en.wiktionary.orgwrong-number
The voice of Love seemed to call to me, but it was a wrong number. P. G. Wodehouse
The truth is everybody does it from time to time. People dial telephone numbers and they get a wrong number only to find that they've read the last two digits backwards. Everybody does it, but dyslexics have this tendency to a higher degree. Bruce Jenner
It was a wrong number that started it, the telephone ringing three times in the dead of night, and the voice on the other end asking for someone he was not. Paul Auster
Doyouwantogoona--Who is this? Oh, I have the wrong number. Delia Ephron
Today, I dialed a wrong number. The other side said, 'Hello' and I said, 'Hello, could I speak to Joey' They said, 'Uh, I don't think so ... He's only two months old.' I said, 'I'll wait ' Steven Wright
Unless they have got the wrong number of zeroes, that house could be a straight $$$ swap for my one-bedroom flat in Tottenham, North London. Source: Internet