Vodafone India — deduction of money

Address:

Paschim Medinipur, West Bengal, 721302

My mobile balance has been deducted twice and when i complained it in the customer care they said that i called someone and they gave me a no. But i never called that no. And surprisingly they have deducted 50 rs for 94 sec of call. First time i ignored and again recharged my no. But to my utter surprise the same thing happened this time, they deducted 25 rs. For a call which i never made from my mobile phone.
Please give a clarification on this issue. I understand that if by mistake i might have called it may have led to balance deduction but it cannot happen twice that too with no call history on my mobile phone.
I am a student living in a single room so there are no chances that anyone has dialed from my phone and later deleted the call history.