So okay, this story didn't happen to me. It happened to a friend (let's call him Bob) of a friend (I will call him Sam).

Bob came to me asking is this a scam and is it legal. Bob doesn't know much about bitcoins and crypto, Sam even less.
Sam somehow got in contact with people who offers to open an account and invest into crypto. These people guaranteed a lot of profit. Sam paid 500 EUR at first and other two times a 2000 EUR.
What is interesting, that these people calling him to invest more. But he has an app (I don't know what app, because I heard it from Bob and he doesn't know either) which shows that Sam has doubled his investment (9000 EUR), but he cannot withdraw it now and these people (from Russia) are calling and rushing him to invest even more.

Bob asked me about that, I said that this is some nonsense. There shouldn't be people calling you and asking to transfer money. All is too fishy.

What should Sam do? Will the police help?