You need to keep arguing, and keep asking to speak to the next person up the chain of command. If your warranty expressly stated the turbos, then you need to keep arguing. Eventually someone they will either help you out of frustration or you will reach someone who will help you because they should. In the mean time, I would suggest you read over your warranty very carefully and make sure it does cover the turbos. If you absolutely get to the point where they will not do anything then tell them you want a refund on the warranty. You should get at least a portion of it back.

But honestly, keep arguing. Don't yell and don't lose your temper. Just keep stating what the issue is, and how you expect it to be resolved. Do not get in to a screaming match whatever you do. Even if they start yelling at you, which they probably will. When they start yelling ask for their supervisor.