Failing to resolve queries.

For May month end I paid R7000 instalment for my vehicle of which my monthly instalment is about R2500. That leaves me with about R4500 in Advance bear in mind that I had about R260 in advance from previous month. Now I called them after paying R7000 to do a capital reduction as I do every month of which I was told that they can only do a reduction with about R2000 and the rest of the money is rebate intrest. Now how do I get rebate intrest if I do a capital reduction every month, every month I get about R1.50 as rebate intrest so when did it accumulate to about R2000 within a month? Where is the rest of the money I paid from R7000? I feel that they have not being fair to me especially that everytime i call them they just tell me that they have logged a call and someone will call me which never happens.