Dispute account balance

Good day, my uncle has an account with Jet Stores in Uitenhage. In January his balance was R2772. Has made total payments to the amount of R1400. He enquired as to why the outstanding amount does not reduce, he was given the run around. The slips also does not show a change in current balance after each payment. Please help, he is a senior citizen and does not have the strength to deal with rude, *********** staff