DMC must pay back all my money. I do not owe or recognise them.

DMC is collecting unauthorised debit orders in my account. I have no active account with DMC, but they collecting money claiming to have bought the debt. The lady on the insists that I owe them and I am mandated to pay them, her debit collects twice the amount it was supposed to take and collects all the amount it finds in my account. It is written that it is supposedly have to collect om 5th, but here they are on the 28th with a debit. How do I report this company, as I have no direct relation with them and do not recognise their position in my debt with TFG.