we make payments but the balance keeps going up

Im actually p***** off by these ****** 1st they keep threatening to take my brothers music system 2nd he lost his job and my mother took over his payments and she has made arrangements to pay R400 every month and which she has been paying for about 20 months if not more which equals to R8000 when she took over in September 2013 the balance was about R5000 guess what yesterday she was so stressed and actually in bed and when I asked her what the problem was guess what the balance is now R6487 and they said she is only paying charges and interest which is R338 per month where is all those R62 difference going to if the balance is instead going up? And then she tells me that my cousin went to EE to show them that her mom passed on 2 weeks back and she was paying life insurance and my cousin was told she has to make a plan and continue paying whats this life insurance for then????? Please explain to me what the **** has my unemployed mom been paying for I mean R8000 already and im not talking about what my brother has paid while he was working so R8000 music system is now R30 000 with charges ????? Im now taking over this account otherwise my mom is going to have a heart attack