RCP Loan that i paid for more than 4 Years.

Good day, i have a problem with standard Bank, i took a revolving credit plan around 2010, i then went back to them and took another loan then my principal debt was about R27000 on 2011, i paid R487 Installment per month before i increased my credit ,after that it never changed i continued paying the R487, after so many years of paying, the Bank now tells me that i only paid interest on my loan and i still owe R27832 by now. I went to the Branch and they said it was the system problem that it didnt increase the installment, they promised me that they will call me on Friday 13th March 2015 but they never did, today on the 20th March, when i call the Head office, they tell me that i must increase the installment and pay until i finish my loan, i ask what about R23376 that i paid and they tell me that it was for interests and i must pay because its my problem. please Help my numbers ***/ *** Brutus