Re-centering should happen even in low speeds
. I take a left-right to enter our Co Car park at about 10 kph. When I take my hands off, the wheel comes back to center.
Take it all the way up to the Senior Man
in the A$$. If they try to convince you, ask them to prove what they say with any other car that is serviced. Get it sorted out.
PS: Send a mail to Hyundai Head Office, ASAP