Sorry, but I still don't understand the problem.
If the item you purchased and the items you returned are on the same receipt I'm not sure how they could have charged you more than the difference... it would have shown as an overpayment. The situation as you've explained it doesn't make sense.
I suggest that you call
Coach customer service to get someone to look up your receipt in their computer system and perhaps they can explain it to you. Also, in future, I would suggest doing separate transactions... just explain to the sales associate that you need to do it for record-keeping purposes (I do it whenever I have a complicated transaction).
Finally, as someone who used to work in retail, let me just say that there's nothing wrong with the store taking your personal information... that's a requirement of any return transaction. Also, it doesn't sound like you had the original receipt for the items you returned. It's not the store's responsibility to keep all their transactions in their computer system, especially transactions from almost a year ago. Perhaps that's why you experienced some "rudeness."