Bad customer relations at Rochester furniture store

I had a 6 months interest free account with the furniture store, my final payment was to be R1529,72, to my surprise an amount of R1697,72 was debited on my account. I tried to query this using the customer service number they provided and it goes unanswered. My details: Absalom Nkosi Cell ********** 097 Email ********** ID no ********** 329080