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TechnoBoy There was a time when nearly all providers were exploited by users. There were tools like PD-Proxy, Tunnel Guru and Open VPN were available and with little tweak either changing the udp/tcp port will grant you access of free internet.
It worked for 4-5 years until Jio came in light and internet became cheaper. I doubt now a days people will bear the pain to look for open ports and edit logs or use a tool to bypass the bandwidth.
If you want to know more about this you can dig deeper.
As far as I remember Port: 80, 8080, 443, 9200, 49200, 49201 used to work most of the time.
You can try nmap in linux and pd-proxy in windows if it still works or search for tutorials in google baba.