Goodness begets goodness

In early November I placed an order for a sports related article of clothing from a retailer based in the San Francisco area.  The item was $99 and shipping was $6 for a total of $105.  I had a $75 gift certificate which would bring my total to $30.
I received the item along with the invoice indicating $105 paid with no mention of the gift certificate being applied. I called to confirm that it was applied.  The person I spoke with could not confirm one way or the other if it had been applied and agreed with me that it might not have been so he credited my charge card $75.
Last week I received the credit card bill and realized that they had indeed only charged me $30 initially than also issued the $75 credit based on the conversation to which I just referred.   (I am not sure why I did not just check the credit card activity on-line when all this was going on.)
Today, I called them to reconcile and return the $75 back that is due them.  Once I explained everything that happened, the response I received was (after a brief pause), “Well, I guess Merry Christmas!”. Apparently, I am the beneficiary of goodwill as it might have been more trouble than it was worth to try to figure out how to show the returned $75 in their systems.
Whether or not they accepted the $75 back does not change my view that this was the right thing to do.  And, I still can’t help but wonder if I should have just written this in a note and mailed them a check.  I will sleep well knowing I made the attempt to do the right thing nonetheless.  The high road paid off – it always does.
Thanks for reading. Have a great day!
Matt G.