iCloud activation lock

Hello! I have a very difficult situation and I would like you to help me. The fact is that I was going to sell my phone. I posted an ad and after a while one person responded. I asked you to check my phone before buying. Saying that she didn't have iCloud on all devices and asked me to log in to her account to make sure everything was working. I didn't suspect anything, I went into her account (since I was selling an iPhone for the first time, I didn't know about the nuances). I tell her that everything works. In a minute, I lose access to my iPhone. She started demanding money in return for a password. If you don't transfer money, it will block it forever. I asked to wait a little and delayed the time. Now I need your help. I can prove that the iPhone really belongs to me and I am its rightful owner. I really hope for your help! Thank you! If you need more information, I will be happy to provide them. I live in Kazakhstan, so all the screenshots and documents are in Russian.

[Edited by Moderator]