What to do if even factory rest can't help?

After downloading a seemingly innocent .apk my phone gpt blocked by a message, which i only could get away by factory resetting. But after the factory reset, I noticed that my phone made strange things, like it turns off when it wants to, it got very hot and even the camery went on on it's own. So i decided to to the reset again. Now i can't get in at all, since my phone wants meto log in into my google account to restore, which i can't avoid, even though i just resetted everything. Bit when i try to log in, it tells my that my password got changed and that i have to wait for 24 h. And i'm getting this message everyday for a month. But the thing is that my password actually still is the same. When i try to log in with a different e-mail, i get an error message. My phone is a s7 with the android version which was the latest in May.

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Can somebody please help me out ?