Telkom *****ing from its customers

I have a modem with Telkom. after not using the modem and not even turning it on, 11 gigs disappeared from my data. i inquired with Telkom why i was suddenly out of bundle. they sent me itemised billing which shows me being "online" at times that i wasn't, or didn't have the modem with me or even had my cell phoned charged. i was still using data i had purchased from from another vendor directly from my phone. after calling 3 times, having itimised billing sent to me again and again refuting the times i had not received any response in 10 days, despite calling and querying via mail. i had not used any of the data allocated to me this month and was terribly shortchanged last month and still no answer from Telkom