Dropped my car off to get diagnosed, they call me ...

Dropped my car off to get diagnosed, they call me at work saying one thing and that they can t do anything, when I go to pick up my car they are telling me they never saw that at all when they scanned it. My car now runs horrible, rough idle and can barely stay on unless I sit there and rev it till it warms up, my gas pedal response is super erratic now, very hard to drive from a stop and it now stalls when I let it go into neutral coming to a stop or going slow like backing in or even pulling up into my driveway and letting the clutch out. Never had a worse experience anywhere in my life and on top of that they charged me $300 to mess up my car. Pretty sure the mechanics just lie especially that guy AC. These guys also asked me to give them a good review and said something about how AC loves his perfect reviews. Now when I call them and try to get it figured out the guy is saying my car is modified but he s saying I have a factory kit from gm which I don t even have and is saying, well you drove it off the lot? Yeah barely it barely turned on the second I got in the car, I even went back in to Chevy before I got my car to stay on by revving it for like 3 minutes straight and told them hey my car isn t staying on and they didn t even say anything about it just said oh the car will run bad if you clear the check engine light. My check engine light came back on 5 minutes after I left and it doesn t change anything. These people didn t even offer me any kind of fix to my problem when I dropped my car off and now that is more messed up after getting into their hands they don t offer me a solution they just hang up on me.