Airtel — broadband bill

Due date of my bill cycle has been reduced from 19 days to 12 days as per airtel without notifying any customer including me. A ticket was raised asking same. 3 rd of every month is my bill cycle and due date 22 nd. Thia month bill generated on 3 rd and due date is 13 th. I am not sure how it became 12 days. Complaint has been ignored and customer care guy says its airtel wish to change plans and no customer should question this. I should pay on time to avoid disconnection.