Overcharged for data

It is the 4th day of the month and my account is already over R4000. This comes after last month I paid over R3000 for it and it was all supposedly because of data usage. After seeing that, I changed sim cards and used my other line but clearly that did not work. I do not understand how in 2 months I can use so much data. To top it all I can't escape my deal due to my settlement being too much, honestly feel trapped in a contract that I cannot afford. At the end of June I will probably be charged R5000? And what am I suppose to live on? I use data but not to the level that I am being charged. My bill has discrepancies such as BIS I do not use, my Blackberry contract ended 3 months ago so do not get why this is there? At this point this CellC buy-back is starting to sound like the only option out