Capitec loan settlements

Hello Peter , my wife took out a loan in 2015 . We paid extra funds into the loan in 2016 to reduce the monthly premium , interest on the credit amount . Capitec refused to reduce the monthly premium R6000 or interest . So Now we are remaining with an amount which can be paid in 7 months with current monthly premium of R6000 but capitec has put 16 months . Why did they refuse to change the credit owedto reflect extra amount we paid and why do we have to pay for 17 months . None of the capitec people are able to help . Should we approach our legal