Credit worx nightmare

Sorry to say this but credit worx is a nightmare, after I received the amount that I needed to pay, I paid it in full, after that all of a sudden there is another amount outstanding that comes out of nowhere? I told the man who phoned me that I am not going to pay that amount, but here it gets worse they charge you for every phone call they make to you, so that is the amount that came out of nowhere is to pay for there phone call bills, guess they will be phoning me a lot as they do already and the bill is just going to get higher and higher and I am not going to pay that amount.