Lack of transparency with contracts

I took R199.00 5G +5G last year. I have been paying for this well, until february 2018. Telkom just started deducting more than the agreed amount. To such an extend that i owe them R1600.00. So they say, how did it get there i do not know.

I tried all possible avenues to get to the bottom of the matter but it was hard, Telkom help centre is a mess and the branches a nightmare with service. I took this small amount because i can afford it, look now the amount of money i owe! How will i repay that amount? From R199 to R1600 within two months? Come on please.

I have to reverse the money every monthend. The lame excuse for the balloning amount is that 'exceeded my monthly limit use of data'. How do i exceed 5Gig deal? Everytime when exhaust the given data is cut-off.