Transmission slipping in new car (2016 Hyundai Accent) after mechanic worked on it

So, I pissed off a mechanic, and when I picked up my car, there are many strange new occurrences.

What could someone do to a car in less that 45 minutes to cause the following? It is a car that you check tranny fluid on the bottom of the car.

-Delayed engagement
-Loud motor
-Rough idle
-Engine shakes
-transmission slips
-RPM up while car not progressing/moving forward
-Hard knock when cold
-Check engine light did not come on

-New, big scratch on car

It is a 2016 Hyundai Accent. It had exactly 38,000k miles on it when I bought it in for new tires. Never had any of these problems before the arguement about price of tires. Engine purred like a kitten. I picked it up, and delayed engagement straight away. Went to 3 different places, and no one found anything wrong, but they sure are telling me a lot of bs, including dealership where I bought it. SOMETHING happened. The place I took it to says they only do tires, so of course it wasn't them. One place tried to tell me that they disconnect the battery from the car to change tires, and the battery in combo with the ECO drive feature was to blame. I am positive the battery doesn't need to be disconnected to put on new tires. My dealer is silent, and all places are acting like I must have not noticed how loud the motor was before. I am very low income and owe $13k on this, so I won't recover soon. Pls do not be like Car Talk forum, and start personally attacking me. I have had enough bad cars to know what transmission slipping looks and feels like. TIA.

I would get the transmission fluid level checked again. Maybe he put in the wrong type of fluid.