Wow. Now this is very interesting. I logged in here after a lonnng time and believe it or not I had what could have been the exact same issue.
This specific dealership that the OP had a bad experience with changed my oil a couple months ago. I drove back home, and the next day I noticed a puddle of oil under my car. I checked the dipstick and the level was fine enough to drive, but clearly the oil filter was slowly bleeding oil.
The dealership tightened whatever they needed to and off I go. They refused to give me any paperwork citing their error unfortunately.
If I hadn't noticed the puddle my story could have very well turned out to be the same as the OP.
I will never take my car for service at that dealership again unless I have a warranty concern. I now take my car to an independent shop in town for service.