Can't pass from google account screen after Factory Reset

Hello everyone, as a lurker, I got many usefull things through this forums, so thank you really, you have saved my neck countless times.

This is my first post, because I ran into a problem and I can´t find a reliable solution for this.

You see, I ofered a service to someone to repair his Moto G (model is XT1543, Dual SIM, 16GB ROM and 2GB RAM).

It was messed up very badly, so I thougth that the only way possible was to factory reset the phone.

After that, the phone, after the wifi selection at startup, asks for a google acount, I tried to log with mine but the phone says that I need to log with an acount used in that phone before. I called to the owner, but unsurprisingly, he can´t remember his email, neither his password.

The phone refuses to boot with any other google acount, it always asks for the previously used, but is missing.

I reinstalled the stock rom, and the result is the same, it seems the problem is server based and not hardware.

I attempted to install a custom ROM, but the bootloader check on dev settings was unmarcked, thus, impossible to acces now.

Am I screwed over? :crying:

Thanks.