BSNL Landline — over bill charge

Sir,
Our BSNL Landline bill was about 3000 last month including broadband charge of 1750Rs. phone charge was about 800Rs alone.Actually we had made very few calls only.We had locked the phone.Yet this happened.But this month we made our phone out o[censored]se by disconnecting lines and we didn't use it at all.But the phone bill was 1500rs including broadband charge of 750rs.It shows that we have made 464 calls! ITS JUST HARD TO BELIEVE IT SINCE WE KNOW THAT WE HAVEN'T MADE ATLEAST 5 CALLS.!
hope that u will provide a solution for this problem.
i would be grateful to you if you provide details of the bill....
yours sincerely
Dr.S.K.Sadanandan