If a dealership ignores an issue that becomes worse, what can I do?

3 and a half weeks ago, I took my car to the Hyundai dealership it was purchased from. I told the service advisors about issues I was having with the engine. They never looked at the engine. I was provided with an oil change, told they couldn't find any issues, and to come back if the issues didn't go away or at the time of the next suggested oil change. The issues got worse and now they want to charge me for an engine replacement when 3 weeks ago I was told the car was running according to coded specifications. During my second visit, I was told that the first time I came in, the car wasn't inspected for the problems I brought it in to be serviced for.