Account paid up, still debited and are mum of what they owe me

I settled the account in December of 2018. They still debited in December an amount of about R1600. They again debited in January 316 plus R109 and this time I was able to reverse. I phoned them to complain about this and said maybe it is the interests. I requested a paid up letter and the statement to show if I owe or they owe me; only a few sentences saying the statement was paid up and were mum on what they owe me. The are just deliberate on this and do not care.