My MacBook is locked by itself and it asks me about PIN code

Try 123456. Also try to clear it from your Find My from your Apple ID iCloud account login.

Take it to an Apple store this doesnt look to be a hard issue to resolve. be more careful to who has got physical access yo your mac when you have guests or are outside also turn firewall on in the settings.

try using all over the pin whatever has been used for your Mac.