un fare billing from my site

Good day I'm hoping you can help me I use to have a loan with african bank I lost my job I couldn't pay them anymore. They handed my account over to depth collectors. A few months ago I received a sms from the depth collectors saying that they are giving me 50% discount off. The amount that I was suppose to pay was R1114. and a few cents and I paid R1115.00 and I was given time till end of june and i paid before then and now someone from credit work called Lorain is calling me saying that I ow them what I dont know she's talking about interest. I honestly don't know what's going on because I don't even have that money because I'm unemployed. As far as im concern i dont ow them or african bank they gave me 50% off and no one spoke about any interest. African bank needs to take care of that not me im done with african bank and it's depth collection department.