vodacom data usage

I received my invoice from vodacom and could see on my statment excessive usage,I could not understand why,my laptop was at times off,and i could see on the billing report that the activeties happen late at knight, and would run for 7 to 13 hrs none stop,my bill was very high, I refuse to pay this account, vodacom claim that it is my responsibility and i must pay the account and then they will give me credits after wards.

Is this possible?