I'm in the US, and I've heard plenty of stories from people who were told by teachers, parents, etc., that they "couldn't sing."

Also, I've encountered people who are absolutely sure that they "can't" sing who do NOT have tales of woe about being told they lacked the ability. Many folks seem to grow up with the notion that singing is just too difficult or too alien an activity for them to even attempt. They seem to have picked up this attitude by osmosis from their families/communities as a general assumption ~ that most normal people can't sing, that singing is just not something that "we" do. There does not seem to be a single traumatic event when the person was singled out as unable to sing.