Airtel — inefficient data pack

I have the rs. 448 pack on my phone. It has validity up to 82 days. The calling is fine. But i have a problem with the data service. After the initial 50 or 60 days, the daily speed of 4g goes down substantially. The signals are shown and the bar is always full with 4g written on the side but the speed isn't there at all. This isn't the first time it's happening. After 50 days, it seems like you limit the usage of data. Please get back to me and resolve this problem asap.