Dealership registration issue

[Jano4]

I am located in Illinois and recently purchased a vehicle from a dealership that made an error on my registration. At the time of purchase they charged me the correct Cook county sale tax, however on my registration they put DuPage county. I noticed this before I took delivery of the car and pointed it out and they said they would take care of the mistake. Almost two months later I follow up with them to see if they have fixed it and they did not. They said they were going to look into fixing it again and now that a week has passed they ignored my latest message to them.

Technically I paid the correct (higher; $1,000) taxes but they went to the wrong county. I can image the dealership pocketing this extra money, instead of fixing the issue.

Has anyone had this happen or know how I should go about it? I wonder if this will effect my future registration as well.