I'm sorry this happened to you. It sounds like someone tricked you into signing in with their Apple Account and may have used Find My to lock your iPhone.
The screenshot you provided shows the regular Apple Account sign-in screen, not an Activation Lock screen. That distinction matters because it doesn't confirm whether your iPhone is still linked to the other person's account.
Please don't send anyone money or share any passwords or verification codes.
I'd recommend contacting Apple Support directly. If Activation Lock is enabled, Apple may be able to help remove it if you have valid proof of purchase.
→ How to remove Activation Lock – Apple Support (UK)
Don't erase or reset your iPhone, as this could result in data loss without removing Activation Lock.
One small note: This is the German-language Apple Support Community, so posting in German may help other members follow the discussion. However, given the expected closure of the German community, similar to the U.S. English-language Apple Support Community I'd recommend reporting this issue directly to Apple rather than relying solely on community discussions.