Exorbitant Data Bill

I was billed for 45GB worth of out of bundle data amounting to exorbitant amounts (R37k). This data was apparently used over a 4 day period. I have 3 lines with MTN (2 data lines and 1 voice line) with a credit limit of R4,000 across all lines. The line in dispute that allegedly racked up this bill has an average spend of R600 since I took out the contract. How I can use R37k worth of data in 4 days, on a line with an average bill of R600 a month...is something that is beyond my comprehension. I lodged a billing enquiry with MTN. I received feedback saying that the data was downloaded from my sim card, with spreadsheets listing sites visited and data downloaded from these site. They concluded that it is my bill and they were not willing to provide any further information such as IP addresses, devices used to connect to my modem as they said they do not keep this information. I can confirm that I am not responsible for the said downloads. I handed in a police affidavit for the case to be reopened and my sim card investigated for sim card cloning. I received feedback giving me the same response - there is no such thing as sim card cloning. My MTN reference is USD***. Pls help!