My car needs repairing but I'm not sure if I should let Carx do the work..I no longer trust them.?

I have a 98 Plymouth Neon with 187,000 miles on it. My 'check engine' light came on 2 days ago and I took it in for an oil change and check up. After the oil change the engine light went off and the car drove fine. When I arrived home I decided to check it because I know my car and I know it wasn't driving to it's full 100%. It smelled like something was burning or it was overheating so I took it back to CARX (where I got the oil changed). The manager was a real jerk. He claimed he didn't smell anything...told me that there are a lot of strange smells in traffic, and basically blew me off. While driving to work, the 'check engine light' came back on...this time I took it to Autozone to get an error reading.....I was told it needs a tuneup. I got a tuneup 6 months ago (from the same Carx) so I called and the manager is saying it could be an ignition coil or anything. I don't trust them with my car. I've had it for 13 years and it's a really good car but I believe Carx is on some major BS. I really want someone else to check the car, fix it (or give me a tuneup) and I want my money back from Carx. What should I do? Any suggestions?