Inflation of interest and hidden charges

I bought bedroom suite for 10500 on end January 2020 at house and home and paid a deposito of 5000 upfront ,I took out a six months hire purchase contract. On 5th February 2020 I paid another 2000 and my Instalment was 1200. This was supposed to bring my instalment down and reduce also my balance. But no that's not the case instead the balance goes up without a tangible reason or logical explanation. It as all blamed on the system