Hathway — Broadband speed drops everyday after 6 pm

I have been subscribed to Hathway broadband internet service in Pune for more than 3 months to a 50Mbps plan.
Every single day for the last three months I have experienced that the download speed drops to 2Mbps or lower after 6pm. I have raised number of complaints for this with Hathway but they haven't yet resolved the problem and keep making false assurances that the problem will be resolved today.
I hence want to raise a complaint against Hathway for this stressful experience. Hathway needs to pay me back the amount I have paid them for the plan but didn't get the promised service. Also, Hathway needs to resolve the problem once and for all as I cannot keep raising complaints every single day