Zone Fitness

I went to Zone Fitness Milnerton Branch in Cape Town to settle and close my account using my card I swiped at their speed point and no formal letter or communication that the account was closed but I thought ok because it was the closing balance we cool. A month later I received a call from Nimble that my account was handed over so I should pay now directly to Nimble. I was so confused as to what more shall I pay, is this account not closed? Only to findout that they handed over my account after paying it off and now Nimble consultants calls me every day whereas I tell them that I've paid... I had to fight Zone fitness to get a paid-up letter and eventually I got it but it's useless because Nimble want's formal internal commutation from Zone Fitness and no one at Zone Fitness is willing to account. I am now listed on the Beurer for money that I have paid and till today Nimble is sending me statement requesting for more money. I cannot convince Nimble to write me off as a customer only Zone Fitness can by proving to them that they received the Money. I have a bad record now I can't even apply for important stuff because if the R1000 I paid long time ago, even when I apply for work, they see my name flagged by Nimble when doing credit checks.