I would say that this is strange...and not right! A few years ago, I tried to exchange an item post sale (needed a different size, as you did), and the SA told me that I would have to pay full price, and so did the manager. The customer standing next to me helped me to stand firm, and the manager *eventually* price adjusted the exchange, after making a big production ("oh, I could get in trouble for this, but I'll do it for you this once"
) . I chalked it up to the fact that it was a brand new store at the time, and had just opened after the Anniversary Sale. To confirm, I contacted CS on-line, and they said "oh, it's not problem at all to exchange post-sale, and we will still honour the price" 
Post this year's sale, I have exchanged items (on-line), by purchasing the new size when it popped up, and then emailing CS, who made a price adjustment for the AS price, and there was no trouble at all.
I'm sorry that you had this experience. It's a shame, both for you, and for the company. If you still really want the items, I would either contact the store manager or the customer experience associate, and talk to them, but I would understand if you didn't want to bother either. Hope you are feeling better post-surgery, and are healing well
!
