Mate 20 Pro, Locked bootloader, USB bugging Disabled, Fastboot non operational

Hey guys im thinking this is a impossible task. So long story short i had emui 11 on a stock Optus carrier phone. I decided to use Hiproxy and upgraded a beta version of emui 12 not realizing that google pay would not work. So i tried downgrading using hiproxy and now the phone tells me device has loaded a different operating system and im unable to fastboot due to not being able to enable the usb degging which i forgot to do.. I dont care about the data anymore but would be nice if it boots up