you went to a crooked dealer alsoYou put 3K miles on in 1 month. Sucks that they put that oil in. Dealers always charge out the ass for any routine work. My first / last oil change at the dealer was over 100 bucks for non synthetic. Might CEL was on too and my car was brand new so I had them check it out. They had to put it on some "special" machine to scan the code that costed me over 60 bucks. All that to tell me there was some dirt in the gas cap. What a rip off. I learned the hard way.
diagnosing "CEL"s is part of the warranty!