Airtel — connection snapped despite making the payment.

We have been duly making payments for airtel postpaid through neft. But they still claim that we haven't made any payments and thereforehave snapped our connection. This kind of harrassment has been done for a number of times. We mailed them and attached a proof of payment. But still we don't find any action from their end.
They are imposing to make payments through airtel payments bank app.