Charged for data not used

I have had a data contract with MTN since December 2013 and have been charged a standard rate of R385 per month for 2 gigs. Once the gigs are finished the line does not connect. I have been paying R385 for the last 19 months with no problems. End of August an amount of over R1700 was deducted from my account, insufficient funds due to only leaving R385 in account. Went into MTN Pavilion 5/09/2015 and lodged a complaint with Nompumelelo Nxumalo at Pavilion, as the data being charged for was not used by us , as we have an open wi-fi line at work. REQ : ***. There has been no resolution to this issue and now the data line has been cut all together. Please can someone assist urgently with this matter as no-one at MTN can help, and this proves to be very unprofessional.