before some months i exchange my bitcoin and they never back my money.
This comment made me confused for a second lol. There are various of legit exchangers over the internet, I bet you even have one locally. If you mean exchanging p2p over the internet then that would be a risky move unless you hire someone to escrow your transactions. On the other hand, it does not have a security guarantee when you exchange Bitcoin with someone face to face. Do you know the risks of exchanging with somone face to face? Specially to strangers? Its risking not only your asset, but your life as well.