I had a very similar experience with a Chase rep almost a year ago. Called to cancel a UA MP card. Got transferred to a guy who was determined to not let me cancel. First he argued about why I should cancel at all. Later he threatened to take away the intro bonus miles. I had read terms and conditions very carefully and was pretty sure that that wasn't possible (at the time; things may have changed). This conversation occured shortly after a pretty famous recording made its way around the internet-- one of a guy trying to cancel his AOL account. AOL was roundly criticized and had to publicly apologize. I reminded the Chase rep of this, because my conversation was very similar. He didn't seem to care.

Bottom line: The card was canceled and I didn't lose any miles. However, the MP card solicitations continue to show up in the mail at least twice per month, one each for myself and my wife.