Billing amount

My airtel postpaid plan is Rs300 monthly charges but from 26-11-17 to 25-12-17 i was billed 386 i.e 86 rupees more of my plan and now from 26-12-17 to 25-1-18 i have been charged 470 and the due date is 14-12-18 then too i have been charges Rs.100 extra as late fee charge and the payment is yet to be made. Mobile number for reference-9022133186