Payment follow ups without addressing the issue

I have registered athe complaint against AIRTEL WiFi for not availibility of 4G network near my area , the 4G network was made available for only 1 month and from 2nd month onwards the speed dipped to 2G only , even with that I paid the Monthly bills promptly , once the same problem persisted even after 3 months I raised complaint with the customer care , spoke to Telecaller and also Team leader for solution, the team leader disconnected the call in between and the problem was not resolved , now after that I stopped using the device and service for past three months even then the service provider is generating the bill, for not using the DATA why should I pay the bill , also the agen who sold me the device told me that there will be cash back of Rs.250 for 10 month where in i recover the Device cost , even that was not addressed , with all this i keep getting calls from bill Recovery agency for payment