Well I can tell you ,but the bitter truth is Indian ISP and LCO care the least about the quality of your connection . I do not mean to discourage you , but you can still try
Your ISP has to have some room left in his Bandwidth for traffic to move freely and peer at multiple places to Internet Exchanged . Let's say your ISP has taken 5Gbps line from some X company . Now he oversells the connections and this leads to slowdown. Hardly any local ISP acknowledges that
This usually happens with Local ISP. National Level ISP like Airtel , Jio Fiber , BSNL fiber , ACT try to avoid this mess and have huge transit with them
That's why it's advised to go with a bigger ISP .
Even if you tell technical terms to the person , he won't understand a thing . Instead you will get frustrated
You just enquire about the ISP and post the details here . I am sure someone must be using that ISP