Direct Merchants Bank MasterCard ..Being scammed for more money

I paid this company off what I owed in full, $1400. Then they said I owe another $70 which I paid, thinking somehow I owed it. Now they are saying I owe another $111 and are trying to say I made a purchase in June, when I haven't used my card and cancelled it before then, so it couldn't have a purchase on it at the time they say.

They have harassed me at work for the $111 and none of their operators have the same story, plus the operators are very rude and unhelpful when I call them. They can't even tell me what I owe the $111 for.

They seem to want to ruin my credit even though I paid them what I owed in full, they aren't happy with that and just want more money. I feel I am in a scam here.