If your phone was reset there shouldn't be a passcode, it should start up as a new device and ask for the Google account.
If you don't know the password for your Google account you'll need to try and do a password recovery on the account which would be easiest by going to gmail on a PC.
It's important not to forget your passwords, especially on a phone, without them the device is essentially a paper weight. Google implemented security features a solid 5 plus years ago making it near impossible to use a stolen device by preventing people from resetting them without knowing the Google account and password.