Bad credit profile because of 20% discount when setting my account, false advertising. My remain balance is still on my account accumulating interests

Home choice are ********** and pretend to be offering good customer service. Guys don't get tempted and accept their false advertising. Last year early December I got a call from them offering me a 20% off when I settle my account, I did that and till this day that 20% they promised to write off is still remaining on my account and it's accumulating interest and I have been getting annoying calls that I need to pay my account in full after I discuss my matter with this urgent they would send me another consulted. My credit profile looks bad because of home choice, they pretend to offer assistance and make promises they don't keep. NCR I don't know if is possible to close down this company because it is only based in Cape Town and it does not have offices anywhere.