RCS Charges

In December I settled my Game Store card debt in full. (administered by RCS) Early Jan I receive another statement stating I had a final balance of R67.00. So I leave this and figure perhaps just a final payment due to early settlement. End of Jan this is debited from my account and my game store account is once again settled in full. Come early Feb I receive another statement saying I need to pay R64. Upon sending a very detailed email on why this is incorrect as they cannot charge Interest, account protection or service fee for an acc which was settled in Dec and again in Jan I simply receive a very daft email stating this is interest charges. This response was also only received after a 2nd mail from my side was sent. Not sure how you can charge interest on a zero balanced account. Along with this I receive a "settlement Letter" in which I am told I have 5 days to pay this otherwise I must make contact for a new settlement value. In response to this I sent another email again pointing these facts out. Shocker, once again no response.