Unaware of open line and data usage

I have contract with MTN in November I apply for additional line for Data only R99, which I was not aware it was open line . The usage was not on zero. My bill supposed to be R235 which end up been to R947 that I had to pay for December unfortunately which I didn't have that Amount on my Account. According to my knowledge if debit order return sms must be sand, I didn't receive it any alert. My lines where suspended I was not informed I just see my internet not working I called customer care it's where I was notified about my other line that was on open line hence I have ask or sign up for Data only not airtime or Sms bundles. Bad service from MTN still am was not advise if I don't pay my Bill it will be double (R1.947.00) the Amount on the 12 January which the day they load data on my numbers which I couldn't access it because I haven't paid. I had to borrow money to settle the bill. I requested the phone recoding where I was advised that my line will be a open line and when data runs out I will be able to have data am still waiting for the recordings. This i my sad story with MTN