I seriously have no clue that whats going on with my case, in the early days on my connection I was getting approx 300 Mbps on both download and upload but facing this issue since last 1 week only. At that time I verified the speeds on google drive also.
The problem seems to be solved for now. They have configured the static IP again, there was some issue with the last configured ip. Getting good speeds now and hope it stays like this only.
Thank a lot guys for your help