iPhone 7 using a lot of Wi-Fi data
Finally, I have found the solution.
I have already turned off iCloud drive and iCloud photos. But for some reason, the phone was uploading my 50+GB data to iCloud drive. When I clicked my iCloud it was showing that there is a Backup in iCloud, the size is not showing up as it is not complete.
But on clicking it, it says 57GB needs to be uploaded or sort of. When I the backup, the phone is now normal, not using any extra data.