From paying R298pm to R5800pm!!! Explanation????

I have been querying this matter for months now! Each time I've called CellC accounts I'm told data validation will come back to me within 48 hours, each call center person logs a new query and gives me different explanations why my account has jumped from me paying R298 to the R5800 now due! I've never had the laptop contract for almost two yrs now and only once have I exceeded the 2GB I get monthly where I paid a little over R400! Their twitter support promised they'll escalate and someone will call me be4 COB 3 days ago but nothing! Battling with this since Dec 2014, they've even stopped sending statements for me to see what's going on! I'm sorry I ever decided to go with CellC! Someone have cloned my Sim(im sure from the inside) and used my line for Internet usage and I've asked for investigation, if you don't come back to me what am I supposed to think? Must I also standby watch my name be spoiled on ITC! Think again! Resolve this issue CellC, ivbeen nothing but loyal and my contract is supposed to end in a a couple of months!