Packet switched data calls

Dear MTN <br> I am suppose to be on a top up contract. This means that I have a set amount that I have agreed to pay you and you have agreed to provide me services. Any additional airtime and data I need to purchase. I started incurring additional charges I went into MTN nicolway and logged a call as you were not giving me my.monthly data plus you were billing me extra they showed me that my line is open I had 1700 spare minutes but both data and phone lines open. (how you have an open line on a top up contract needs explain. But due to mtn on strikes nothing gets solved). I closed the line anyways reference 129 608 072 . This month end of July I have just need billed R 1,192 additional for packet switched data. What the he'll is packet switch data how am I using this when I am buying data from my standard bank account. I am closely watching my data balance, I do not know how I am paying so much money. My top up contract is R451.60 cents per month and now I am billed in total R 1,803.8 cents. How does this happen!.I'm absolutely upset and have no clue what these charges are for it requires and explanation. And a refund. ***