I start from the principle that people I don't know in real life should not be my "friends" in this game either. Some people only want to befriend you in order to know your fixtures, allowing them to reschedule their home games against you to a time (very) close to your previous game, preventing you from having rested players...

As for the question of the OP, if Nordeus Support don't help, just keep your answer pending until the end of the season and reject the request on day 1 of the next season. He won't have any interest any longer.

Possession bonus received from people supporting you is a big joke in this game anyway. I lose like 70% of the games where I have people supporting me, and I kick the arses of teams having even 10 people supporting them.