Vehicle finance debacle

I bought a car for R189000 - and took out a loan for that amount at 11% interest over 6 years. 3 days later I sold my old car for R100 000 and put it into my loan account - expecting the original amount of R180 000 to be reduced to R89000. Instead they put the R100 000 against the final balance that I would have owed over the 6 years HAD I NOT paid any extra back which mean my balance ended up being R160000 - they effectively put R20 000 of the R100 000 against the car and took the rest as interest for YEARS THAT HAVE NOT OCCURRED YET!!!. THAT IS *******! I have emailed twice and called twice- the first call said yes I was right and they would log a request to back office, the second call said no request had been logged and then - after an hour on the phone - they said they couldn't log a request as ALL THE SYSTEMS in he entire call centre were down - and I had to call back later!!! I am at my wits end! I phoned my dealer and they are horrified and promised to try and help - but I thought I would try this too.