I feel oppresed and taken advantage off.

I took a 2 year contract for data which ended in Feb. I went to the shop to cancel the contract and they gave me the number to phone. The number was unreachable i only got help in April. Since April im being harrased by the consulants that tells me i owe cell c cause I did not cancel the contract. They say i was send data and i could not access it as it was locked. I was paying R200 monthly which i was paying before they give me data. Now out of nowhere im being charged R349 for the data I could not access. They deducted over R900 from my account and they say I still owe them R349. I feel ********** by cell c and Im from a disadvantaged family.. How can I pay for something I cannot access How can the premiums go up with 75% after the contract ended. Why am I given the data that I cannot access cause I used to pay before given the data Who can assist me ?