Dear Samsung Member,
Greetings from Samsung Customer Support!
To resolve your device network issue please visit this link: https://www.samsung.com/in/support/mobile-devices/samsung-mobile-network-issues/#:~:text=1%20Check%2....
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Samsung Customer Support
Slow internet speed issue is not a user specific, like me lot of other customers are facing the same problem with M31 mobile, but Samsung doesn't care about the customer issue. I have also complained multiple time, but not resolution till now