Debit order problems

My debt has been settled but two months afterwards and there is still debit orders going off on my account. If I contact them, they say that I need to send a proof of payment but it's a debit order. If I send a screenshot of this debit order, they say it's not good enough please send a proof of payment. I already paid my debt, I informed them I settled everything and also supp**** settlement letters although they get paid admin fees so they are able to phone to collaborate that it's been settled. The help given is minimal and the solutions they give does not solve anything. How do I get my money back for the two months that they deducted after I settled my accounts?