iPhone 7 using a lot of Wi-Fi data From 27th October, my iPhone started using a lot of Wi-Fi Bandwidth and I cant use the Wi-Fi for any other purposes.
Things I checked:

Checked for Whatsapp chat backup, No.
Checked for Translate offline languages, No.
Checked for iCloud Backup, No.
iOS update, No the auto update is off. Currently using iOS14.0.1. Since all bandwidth is used I cant update it manually also. So I didn't try.
Auto App-Update, checked and it is already Set to Do not auto update over Cellular and Wi-Fi.

After all these steps, still the problem is not solved. So I reset my iPhone deleting every data.
Then I restored all data from iTunes Backup and tried to download all app and it took a huge time and lot of data because something is running in background. So I paused some of apps from downloading and then cancelled the download of these big apps like Apple Office Apps, Google Office Apps and MS Office Apps and Garage Band.
I had a lot of photos and some files in the Files app in On my iPhone part and not in iCloud Drive.
My iCloud drive and iCloud backup is always turned off. 
Then I deleted all my Apps to check if any app is doing it.
First whatsapp and then every other non-apple apps + Watch app and Translate app.
It didn't work.
So Today on 3rd November,I deleted all the files in my On my iPhone in files app and deleted all my photos.

Now the phone, despite having nothing, is still using all the Wi-Fi bandwidth.
There is no way to check the Wi-Fi usage from iPhone. But the battery information shows this data.

I have never tried with Cellular data since I don't have a Cellular plan and this king of data usage will cost a lot of Money if cellular data is consumed.
Also, now randomly, the phone is getting disabled for 5 minutes, mostly when I press the power button or when I restart the iPhone.
This is not Jailbroken or anything.
**Do anyone experience the same issue, or anyone advice me to solve this problem.
**
I would really appreciate it. Thanks in Advance.
Update on 4th Nov
I have already deleted all apps other than Apple apps.
Today, I deleted each app of apple and looked.
When I delete the contact app, the wifi usage became zero.
Now I am going to do the restore of my iTunes backup and delete the apple apps and see how it goes.
Update 7th Nov
Still the same problem of using a lot of Wi-Fi data exists even though all the apple apps are deleted.
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.