Virus - Can Survive Factory Reset

My phone is really slow, so I can't explore,sorry if this is in the wrong spot.
I've been attacked by (I think) a virus on my phone for a while now.

Device info:
Samsung Galaxy J3 Prime
Model: SM-J327T
Android version: 7.0
Can find more info if needed

Virus info:
Origin: Unknown, but it appeared at least a year and a half ago
Symptoms:
Random things will stop ("System UI has stopped working", or Samsung keyboard, or Discord, etc.)
The device will restart randomly. It won't turn off, just suddenly freeze, go black, and turn back on. Sometimes it gets stuck and I have to take out the battery, and put it back in to unstuck it.
"YOUR DEVICE HAS BEEN FLASHED WITH UNAUTHIRIZED SOFTWARE" The virus, I assume. Goes away after a few minutes.
"This device has been encrypted for security. Please input password to unlock"
Finally, eventually, my phone will start up saying "Erasing..." and factory reset itself. Currently on the third reset, so I'll do literally anything to fix this, even if it means losing what little I have left available.

So uh... that's all. I can answer any questions, and if anyone knows how to fix this stupid thing, I would kiss you if I could. Well, probably not, but you get the idea.