*****ing money

I have a Vodacom 2GB Data Bundle which has not been used in September 2017, and Vodacom has deducted an amount of R 8500.00 from my account stating that we have used the modem in August 2017 for 2 days and that the amount is R 8500.00 for the two days. They have taken the money from my account stating that we used the modem, where the modem was in a laptop bag at my office, not even been taken out of the laptop bag, for we have ADSL. Now Vodacom states that we used if for G-Browsing that they don't even know what it is???? They can not provide us with any sustainable information that proves that we used the modem!! Now they have taken the money from my account which is in excess now because of them. Please help me.