Seems like I'll never stop paying this loan!

I had an account/ loan with Capitec Bank,which was handed over to a Debt collector (MDB). They phoned me to make a monthly payment to settle my account/loan it's been two to three years;if I'm not mistaken- however the balance is not reducing. They take the re-payment and reflect it as interest on the statement reason for this, they say the payment I was doing was to keep the account not to be handed over to the lawyers. My concern is: * The balance is not reducing and it seems like they want me to pay them forever. * That,why have I not been told from my first payment that I'm paying off the interests?