airtel fluctuating SNR margin, frequent disconnection


Last many months I have been having this problem of airtel fluctuating SNR margin, frequent disconnection, after complaining things get sorted out for a while before starting once again.

Complaining to airtel is not working as their staff is giving standard answers.
1. Computer network card problem, changed that but problem remained.
2. modem power plug problem, changed the power to usb power cord
3. modem itself changed
4. now they are saying line coming in house has wiring which could be faulty, they want to bypass that & bring external wire.

Problems I am facing are as follows
1. fluctuating SNR margin both for upload/download
2. frequent disconnection even when the ping is perfectly fine both to modem & server
3. irregular ping at different time of the day

Before I get this external wiring done I have read that wiring can indeed be a problem for frequent disconnection but cant this fault be pin pointed with a testing meter? these airtel guys are saying all this verbally they come without any kind of meter to check the line. I live in a row housing where airtel has internal wiring for whole complex, then outside each house they have installed a DB box from where they connect to our internal wiring.

I am attaching few screenshots so you can see the fluctuating ping & SNR margin.

Even when there is fluctuating ping & SNR margin is stable & high I loose internet & on modem 3rd light is visible ON. Switch off the modem for 2 min & switch on it starts working fine again 50% of the time.
I am lost as to what is the problem, need help!