******* not explaining the contract - data of 6000

I renewed the contract (in March 2015) with them from a little note book of 5 years to a tablet and we asked them to limit the data not to be open for our daughters use for homework as she is in grade 11 now. They did not explain properly that this was not a limited thing. The 1st month of April my daughter ask that we buy her data, because the data was finish we told her to wait for the next month until she gets the 500 or whatever amount of data because we did not have money to buy. I did not check my statement that comes via e-mail because of numerous mails that I have to read daily. They said this was an open contract after they deducted 3324.32 from my bank account. Why didn't they suspend this thing the 1st month, because no money went of my account to them for 3 months they only deducted 99rand. Now they say I owe them plus minus 6000 rand. Where must I get this money. I'm sole breadwinner and my husband is studying fulltime. When I phone 808 they don't respond. I hang on for hours on end. Its torture...I cannot take this. Me and my husband asked them nicely not to make this a open thing but a prepaid. Why did they not do this and allow this thing to carry on.