Billing

My contract came to an end last year March. I was unknowingly still being billed for something at the cost of R160? I reversed my debit orders and had agents call me and ask me to pay for my account, when I asked what the R160 was for, they claimed it was for data. I didn't receive any data! I had been buying my own! I am now being billed R700, sometimes over R400. What is going on?? I might as well be paying for a new phone, rather than sit with an S8 and pay the same price. Ridiculous.