If the group is still active you should be aware, that the mods and admins of any group are free to remove any member at any time just because they feel that person should not be in that group. Normally this is in response to rule breaking, but it doesn't have to be.
There could be any number of reasons you were asked to leave.
- personality clash with other members
- comments not appropriate to the group
- not contributing enough or too much
- repetitious posts or conversations
- self promotion
- incorrect age group for group, or level of maturity
- negative personality
- mocs not part of main subject (halo mocs in a star wars group)
- mocs not in correct format (LDD mocs in an actual bricks group)
some of the things in this list might not break the rules in most groups, but could be enough for an admin or mod to feel you don't belong in THAT group.
You probably will not get any help from sean or any of the other admins here because (as they keep telling you Oliver) they have no power over other groups.
Sorry, but it's up to the admins and mods of the group that banned you to decide whether you can return. It isn't up to anyone else. So please stop asking.