Settlement fee refused

I had an account with Markam I was promptly paying my instalment well till I had a loss of income and I reported that to markam store. pleading them to understand my slow paying method and a shorter fee, then on my surprise the debt was handed to mbd attorneys. Then since from July started paying markham store a fee of 100 rand because its a fee I can afford, the problem is the debts amount of R1.5 is still not goinh down and when the mbd consultant called me, they told me that the bill won't go down and arrears will be imposed cause i'm paying at the wrong shop. Then I pleaded to be transferred to their superiors for arrangement purposes, I asked the mbd to superiors to kindly give a settlement fee so that I can pay the amount then they decimal refused. They told me that I don't qualify for a grace but I wasn't given any reasons. So my problem why did markham accepted my payments for more than two months of they regarded as the wrong pay point? Why don't I qualify for a settlement fee? If my bill its so little in sense that it qualifies for no settlement amount why don't theu write it off then??