Unfairly treated

I joined gym company 2014 and move to Pretoria 2015 and the was no gym company in Pretoria by then but I still paid the gym because I had a contract with them, then when I had chance I went in gym company newtown where I joined and I was given amount of settlement...yesterday I received a WhatsApp message that I’m blacklisted.... I followed up today the lady that I was dealing with she was very rude and she ended up saying I’m owing R6000 my question is all these years why they were not calling me , and I always have money in my bank if the case is that R6000 was built by R 300 that I reversed after I paid the settlement....