That's really sad dude, I think your PC might be infected and since you didn't had 2fa enabled they took advantage of that and stole your password or cookie and used it to clear your account.

I would suggest, take necessary back up of your important files and do a clean install of OS and make sure you enable 3fa, which is when you enter your 2fa code from the google authenticator they would send a code to your registered email which you have to enter at LBC and only after doing that you'd get access to your account.

And then it would be really hard for anyone to get into your account.