Goods bought in 2016 over 24 months and still having a R1027 settlement amount in 2019

I bought a microwave and a washing machine on 21st December 2016. Payment period was for 24 months as stated when buying on account.

I went to Game Promanade in Mitchell's Plain and they told me that I still have a balance of R1027 to be paid. This payment should have been finished 21st December 2018.

I want them to refund me for extra charges.