01-31-2016 07:49
01-31-2016 07:49
01-31-2016 10:14
01-31-2016 10:14
Welcome to the forums @SuperBlonde2000
Normally a person would have to be your friend to invite you to a challenge. I've noticed after a challenge is complete, it lets you do a rematch. That way, even if someone isn't a friend, they still get the invitation because you had been in a challenge with them.
Could that be how you're being invited?