Uncommunicated billing

1/5/2015 my debit order bounced I received msg with the returned amount of 743 from cell c which is the amount I never signed for in the first place ... Im a a lots client to cell with 3 contracts with them .,, but what they did now is not tolerable ... I contact them 25/5/2015 to try and understand why I was billed that much I spoke to delmaree who logged a quiery ref*** which was suppose to take 24-48 on Sunday 31/05/2015 called back as there was no feedback yet from cell c .... Only to find out the quiey was not yet attended to ... On Monday a guy called Tebello called me he tried to explain to me why I was being billed 743 while I signed for 517 when I took my new contract he said in April 2014 I requested for extra data which according to their billing 1 data cost 149 but me I was charged over 200 for that extra gig 517+226=743 ... I want to know why I'm I paying that much and wen I took a new contract at sandston mall cell c Yusuf said I'm only gonna get 2 gig 1 gig day time then the other at nyt so according to me that was enough as the line was no longer as open like before ... But somehow things changed ... I need to understand why I'm I being billed over