I'm sure I played you yesterday if your name is Kluiverte online as well;
can't remember if you're the bell who I went 4-0 up against within the first half hour, then the person started being a bell and scoring own goals; not too sure but i do remember your name from yesterday, so sorry if it wasn't you.
ANyway; to get out of a group, when you go to a lobby, you should see an option called 'group'. It'll be under the likes of 'view data' 'rankings' and all that bull.
Once you get into this 'group' option, the very last option should be 'withdraw from group'
Leave a reason(ie group is wank' then you're free.