Airtel Postpaid - Problem in network

I am using airtel network above ** years and from the last * years, I am using postpaid. In my area the network is not proper and no proper usage. I have raised the complaint in **** but nowadays no one solves my compliant. So I asked my customer care what is my compliant status he says work under process. How many years work going on? In my working place, talk time call cut automatically. I am searching for a new job when some company called in my phone it was not reachable at the moment. Nowadays I am using one and only Airtel. Every month I pay the bill on the correct time but they don't solve my problem. The first time when customer care says that your phone has some problem I changed to Lumia *** to Nokia * to Nokia * within * years then another customer says sim slot problem I changed sim also but doesn't solve my problem.
So please kindly solve the issue otherwise I need a correct solution.