This is why everyone in the forum said you not to opt for AirFiber. If you have optical fiber (cable connection) in your area, it is more reliable compared to AirFiber.
AirFiber is mostly preferred in rural areas due to no feasibility of optical fiber connections.
The issue got resolved by the technician on the same day i posted here.
The issue was due to the installation guys who installed the ODU to IDU with the old existing ACT cable which was swelling water inside without my consent. They were busy in watching reals and talking in phone without dedicated work.
Due to this on same day itself router adapter got malfunctioned and replaced with new in few hours. And the new adapter was also getting short circuit during afternoon.
The service technician was very helpful and he is 30+ years experienced and he replaced old cable with new, and also raised a complaint against installation guy to not repeat again for any new installation.
From last 3 days no more internet issue and speed is upto my cap.