chloe wb

So I recently bought a 2017 audi a3 automatic sportback, within a few days the gearbox malfunction light came on. The garage took it in and fitted a new mechatronic unit. Since having it back its still not right, when I come to a stop and the start stop kicks in, when I press the accelerator to get going the car moves about a foot before shunting forward and then getting going. Its that forceful that the first time it happened I thought someone had smacked into the back of me. Its been back into the audi garage and they said they just forgot to reset the car after fitting the new unit, so did that however it's still doing it so it's back in with them again.
Has anyone had this or know what it could be as I've never had anything like that before? I've put a video up so you can see what it's doing