I've been there and faced similar issues so I can understand. I've managed to get back a working internet line but it's not running upto max speed. Waiting for a new router in hopes of solving my current issues now. The early days of lockdown until April was a nightmare. Day time the speeds had dropped so bad that it was hardly useable.

Haven't faced issues like that since I left BSNL 6 years ago. Anyway, If by end of this month I can't get a stable 100 mbps from my new ISP then I'm going to try JioFiber which is my last hope for my area.