Airtel / Postpaid — one time charges with mobile bill

I m the the user of airtel postpaid sim. Every month i m paying my bill without default, last month also i have paid my bill through online, within rs.800 i was receiving my bill, but this time i got bill including one time charges, my bill amount is rs.560 but one time charges is rs.3245. I dint understand why i got such bill. Please take my complaints i m not going to pay one time charges, i m not able to pay this, please do the needful.