Excessive MTN Billing Account

My services is suspended and I cannot get through to MTN to help. My bill is normally R439. I was billed from R1200 in April 2015 to R5836 in June 2015. Today I received a sms stating that if I dont pay R2611.18 immediately Legal Action will be taken. I cannot use that much data when I have wifi and Cell C data. Numerous phone calls and emails from 29 May 2015 were sent to MTN where I requested the itemised billing of where we went over the 2 GB of data. I refuse to pay any amount before they can prove to me what data has been used and downloaded to the amount of R5836 in 2 months. When you phone the customer care number their services are suspended.