Just do a factory reset once more, then immediately install the firewall.
Do not use Google Play Store for this.
NoRoot Firewall
https://noroot-firewall.en.uptodown.com/android
Then IMMEDIATELY turn off the internet access for Google Play Store.
What we are doing is trying to prevent these apps from reappearing.
Google is always my first suspect.
In fact, if you csn't beat Google to the jump, then download the apk for NoRoot and put it on an SD card.
Then do the factory reset.
Turn the device on, but do not turn on any radio access- no Wi-Fi, no cellular, nothing.
Put it into airplane mode.
Put the SD card into the device, and install the apk.
Open the app and start it.
A key icon should appear in your status bar.
Select Apps at the bottom.
Block all access for Google Play Store.
If that E-mail app appears in the apps list, block it.
Block Google Partner Setup.
Block anything you distrust.
Notice that there are two areas for each app to be allowed/blocked access- Wi-Fi and Cellular.
If something on your device won't work later on (the clock, for instance), then you know you can go back and grant access where needed.
You can't hurt the device with this app, only limit it.
You can do an internet search for any of the apps on that list to try to help you find out what they do.
One thing you do not want to block is Google Services Framework.
If this keeps those apps from reappearing, then all you need to do is keep NoRoot running.
You can start by going to Battery Optimizations and bnot optimizing NoRoot.
Make sure that you tick the checkbox on the homepage of the app for Start On Boot.
Unfortunately, it is not a native app, and so will probably stop at some random time.
Blokada will probably be the best choice on your device.
But, this will let you see where the apps are coming from, whether it is from Google, your carrier, or other sources.
You will need to unblock some things to make functions work, and most likely will eventually unblock whatever is downloading that bloatware.