Unpay

Pay her the debt you owe her, and unpay the villany you have done her

Source: wiktionary

'It seems to me, young man, that you are rather particular as to how things are done for you. If you had begun to be just a little bit as particular in making the debts as you are in the way of having them paid, there would be a little less trouble and expense all round. However, the debts have been paid, and we can't unpay them. But of course you can repay me the money if you like. It amounts in all to four thousand three hundred and seventeen pounds, twelve shillings and sixpence, and I have paid every penny of it out of my own pocket. If you can't pay it yourself, perhaps your father would like to do so.'

Source: wiktionary