What would Mike F. have been able to do for you?

I suspect that the people working at a specific airport would not be able to take a credit card number over the phone.

While you should have gotten the correct information originally and while it would have been nice if the people at Hartford had caught on that you thought the surcharge was for both flights and not just one, Mike F. was pretty much in the position of not being able to do anything except accept payment. If you weren't able to make payment (given that you were far enough away that you would have needed an airline ticket to get there with your credit card), I can see why Delta wouldn't want to encourage you to have a long angry phone call with Mike F. about things he wasn't involved in and couldn't fix. Whether or not Mike F. was engaged in urgent company business at that exact moment, he has a job that involves a lot of putting out fires, and therefore they want to insulate him from time-consuming things that are not part of his job.