Sold A Car To A Dealer. They Gave Us A "we Owe" For The Money And Are Trying To Back Out.

TL:DR had a car that had mechanical issues. Took it to dealership to fix. Took them 5+ months and multiple tries to fix it, including things they messed up. After it was fixed we asked if they would buy it. They made an offer. They signed a we owe and we signed the power of attorney to transfer title. They said we could pick up our check the next day. Now they're trying to back out. Is this legal? Should I get a lawyer?

Longer version:

Car is a piece of shit 10 year old Kia. About 5 years ago the engine blew and we had it replaced through the dealership warranty. The mechanic at the time has to go through Kia to find a replacement engine.

Fast forward to January of this year, the car dies on my wife while driving. We take it to the Kia dealership(not the one we bought it from and not the one that fixed it last time). They take over a month a $2500 to fix it. We go to pick it up and it does the same thing on the way home. So we take it back.

They "fix" it again. My wife drives it for a week and it dies again.

They take another 2 months to get an engineer from Kia out to diagnose. Turns out the replacement engine that Kia gave us last time was 3 model years older than the car itself, and the parts the dealership replaced weren't the right ones. So they had to use the older model year parts and finally fixed it this past Monday.

During this 5 month period my wife bought another car, with the intent to get rid of the Kia when it was fixed because at this point it's beyond unreliable.

We ask the dealership yesterday to make an offer and the come back with $4,000, which is fair. We hand them the title and keys and sign the we owe and title transfer paperwork and they say we can "come in tomorrow to pick up the check". They didn't tell us this until after we signed everything.In retrospect we probably should have told them to eat shit and give us the check before we sign anything but I thought "it's a dealership, not some random person from Facebook,, they'll pay us for it."

Guy calls back today, says they were "unaware" the engine didn't match the car, despite this being a months long ordeal and working multiple times with the service manager who I'm sure signed off on the trade in inspection. And says we need to pick it up and hangs up.

Do I have any legal recorse on this? Small claims court? Anything? Or is it not worth it and we should just try another dealership? The offer was a fair offer and I'm legitimately tired of dealing with this piece of shit car and just wanted to wash my hands of it.