Asking for payment without bill

I have been a Airtel postpaid customer for more than an year. My mobile no. is 9212711163. I changed my network provider to Vodafone in June due to bad service from Airtel off late. Now, they have given one more example of customer harassment. They have not sent me any bill since May but are asking me to pay an amount of Rs. 1344/- as payment for services in May. When I asked for a bill on customer care, they said that they wont give me a bill and cut the call. I approached customer stores of Airtel but even they did not give me any copy of the bill. Now, since evening of 17.07.2014, they have cut my connection and are not ready to take my complaints. According to me this is customer harassment as I don’t think that they are allowed to ask for payment without bill. Also, when a customer demands bill, he should be given one. I do not understand their logic of withholding my bill till i pay the dues. Only reason I can think of is that Airtel people are miffed because they are losing customers to Vodafone and may lose more if this continues. Unfortunately, I will have to give in their to their cheap tactics and pay the dues. But i wanted to highlight this issue and point to cheap tactics by this company. Hope some action is taken against them.