First of all, forget the BBB! They are an absolutely useless and corrupt organization who has absolutely no power at all to do anything for you.
FYI..."Black mailing" is 1 word. "Blackmailing". Totally different meaning.
The only question here is whether or not you had a legal binding contract with them that you did not satisfy. That is the only valid issue here.
Do you have a contractual obligation with them?
If so, it was you that engaged in the "rip off" here. If not, just tell them to put you in collections so you can sue them.
This is black and white. One way or the other.