Let's do it by steps:
and there was a guy who said that he has a private group
Who is this guy? You must post here in the forum.
but it costed money to join.
How much did you pay? You must post here and show proof
I tried to contact him several times, he is just ignoring me. From his informations, I have only his IBAN and his FB account.
You should report your case to the police and show all proof that you have for the police to find the scammer.
Can someone help me what to do in this situation?
report your case to the police