Similar thing happened to me a few weeks ago - someone in the US registered for a Postmates account (as a delivery driver or something? I dunno) with my [firstname][lastname]@gmail.com email address. Quite how this was achieved without some sort of "Follow this link to confirm address you've given us" email, I am not sure.
Took more than one attempt to get Postmates to understand the situation. Their first reply was along the lines of "Sure, we'll just need your Social Security number to verify that you are the account holder, and we'll deactivate it for you".