Consumer Redressal

Hi, I have brought a dongle from airtel on 26/4/2015, it was working fine for couple of days and then it was not, again i took that to airtel outlet where they said, there is some problem in simcard and they have replaced it, after that again it worked fine for couple of days then not. i have complained so many time in customer care but they just saying they are rectifying it, but its never rectified, but they have sent bill for 2500₹ when i spoke to them again they are saying its monthly rental. If its not working then why I have to pay, if its working i m ready to pay the bill. I brought this dongle thinking i will work from home which I could not able to, also spent money on dongle again they are sending bill for no reason. and again I have to explain whole story to them every time, then there is no solution from their end apart from bill. Please do the need full ----- Thanks Harish - Mobile - 9845916542 / Dongle card no. 7899706778