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?
Assuming that you belong to somewhere in Europe because you are saying your friends paid EUR. I think you may go to the police this definitely is a scam no legit scheme would invite you to bring more money like this. If they could have been selling some service or bot or API to earn profits even then I would have tried to have second look on that app but this definitely is scam. Police might just help in tracking down those people(What if they are from your city only using proxy of Russia isn't difficult). But if they are really from Russia then I don't really think anything can help you just try customer support if this site does offer any and ask them for money back.