Payment arrangement nightmare!

I opened a CTM credit account in 2015, and have been paying the installments in full since. Then in 2018 I met some financial challenges and called them to let them of such. Instead of paying the R1500 I was paying, I told them I can only manage to pay R500 every month and no longer use the card until I close off the account. All was well until early this year when they handed my account over besides the arrangement we had. Now even the collector is trying to force me to pay huge amounts that I can't afford. I have since stopped using that account 2 years ago but interests keep going up on it even though I'm paying the R500 monthly without fail. So ****ed off!