Airtel — Monthly billing issue

We have been using airtel broadband and mobile phone numbers for a very long time now and in march 2020, we decided to switch to the new one airtel plan of rs.1999 plus gst which includes fiber broadband connection, our mobile phone numbers and airtel xstream dth. They were supposed to change our billing plan right after we requested to switch our plans. Instead they didn't inform us about any changes and started charging us extra on our previous plans and after two months of back and forth with the airtel store nearby they finally changed the bills. This time they've charged us a whooping amount of 4455 and they claim we have payments due from the previous month. Our bank statements show that all payments have been cleared. It clearly is their fault and they are charging us extra for no reason at all. And they even have different reasons everytime we contact the customer care. We have been trying to have this resolved for months now and nothing is being done.