Thrice burned and burned again

Woolworth's shopping experience has always been excellent, so when they offered me a loan through Woolworths Finance, I had every confidence that the experience would be the same. Due to an unfortunate sequence of events, I had to repay the latter part of my owed balance through third parties. When I noticed that it was not working, I notified Woolworths, but I was rebuffed. I did, however, pay the balance - according to my calculations, almost twice what was actually owed. It is now several years later, but I am still being contacte by collector after collector. When I contact them, it seems a short while later, Woolworths just gets a different collector to contact me. I have tried to contact Woolworths directly, but I am either ignored or told to contact the collector du jour with a proof of payment from the previous collector (who didn't follow up on my proof or even bothered to respond) These people falsely list me with credit bureaus and the last one even decided to contact my employer to tell them I am a "bad payer". Woolworths has since withdrawn from the loan business, but they are still harassing me. My advice to anyone reading this is: unless you can hold it in your hands, don't buy anything from Woolworths.