Double interest on loan accounts

It came to my knowledge that I have been charged double interest on my loan accounts, the monthly payment every month includes fees and interest, then I have seen that the total will drop, at the end of the month a further amount is deducted off the capital amount, I've been told this is further interest, therefore my monthly payment does nothing to the capital amount and makes it nearly impossible to make any headway on the loan. Capitec have not helped or answered my follow up emails. This is an amount that is not told up front and now when I query it I get no response.