Deducting huge balance without any activity

Today after 3 ‘o’clock i show that my balance was deducted nearly rupees 110 and when i called the vodafone complaints they said i used the net and due to which i was charged this balance but i did not use net for last few hours and also i have 3g net balance activated. HOW CAN THEY SAY I WAS USING NET WHEN I DID NOT USE AND NOBODY TOUCHED MY PHONE AND IN PHONE ALSO THERE IS NO SIGN OF USING NET FOR FEW HOURS.