Billing

I have a problem a mobile contract with Telkom. One month my debit did not run because I requested change of banking details. Although I notified them of the debit that did not run they decided to disconnect my service. They asked me to pay R800 which includes reconnection I think so and I did. Take note that my monthly bill is R500 but now they say that my bill for month end R700. What is it for? I complained and promised to come to me but didn't. I have a reference but their 180 and 10213 doesn't put me through to the relevant department.