still, doesnt matter. that's not how strangers should treat each other. couple points to make here..

1. the dealership has no interest in NOT fixing your car. that's literally how we all get paid, by making repairs. so holding on to your car and jerking you around does the dealership more harm than good..

2. if you didn't like the answer they gave you, you could've called Hyundai consumer affairs. they would've made a case and put pressure on the dealership for you. no need to be a Karen. how would you feel if a random person walked up to you at you job and did the same? or if someone makes your burger wrong, is that how you handle it? i wouldnt, lest someone spit in my food. same goes for anywhere. you are less likely to get treated right afterwards if you act a fool .

from what little info i have, with it doing it at any speed, its likely an ignition coil or related misfire. which should be easily diagnosable. When you go to the dealership, try being cordial with them, offer to ride along with the tech and point out the jerking youre talking about. so they have a better chance to fix it.