Service suck from Nimble Group.

I am very confused and totally disgusted with the service I'm receiving from this company. It's not the first time and I'm really hoping it's the last time I ever have to deal with them. I requested a settlement amount which I received and was due on the 22/07/2020. My banking is set up for an auto pay which I did not stop I will take responsibility for that. I then paid the account up in full less the 2 amounts which was paid automatically. They are now telling me I owe them a further 2000 and I made an arrangement to pay R100. I never made this arrangement. I am trying to call but the line keeps cutting. I just want the file closed and itc updated as I'm in the process of purchasing and securing a bond but it is impossible to make contact with this company. Please can you advise what my next step would be as I have tried emailing, iver tried calling and I've tried using their whatsapp platform.