Update!
so the battery didn’t do much, I’ll probably keep it tho as it’s the right one, after lots of swear words and telling the car to find another owner I managed to swap the ecu out, which isn’t in the boot in the mk3 it’s actually under the hybrid system in the engine bay, and no I didn’t enjoy working around that!
I’ve swapped it out and the fault went out instantly, ill have to learn how to calibrate it to my car I guess, but proof will be in the drive later today and see how she goes