What's wrong with my car now?

It's a 2014 Ford Focus. I had some kind of oil seal replaced because there was oil leaking from my engine. It was covered under warranty and completely free. I got it fixed and when they returned my car to me its accelerating really loudly and doesent go. I returned it to have them look at it but I'm just curious what it could be. Like it sounds like a truck or hole in a muffler

Probably had to remove part of the exhaust to access the seal and they created an exhaust leak.

How is it accelerating if it doesn't go?

They didn't connect the exhaust back properly. They'll need to do that over and use a new gasket when they do. Take it back to them.

Take it back for another look. Get the manager to drive it if they you the run around.

They blew apart your decrepit exhaust system with their hot rod driving on the lot. I would take it to another dealer.