A silly one.
Years ago I worked in Customer Service for an upscale regional department store (now part of Macys; I don’t shop there anymore), fielding calls primarily from store associates who needed an authorization on a store credit card purchase, request a credit limit increase, etc. But we also occasionally got calls from customers with questions about their accounts (most of these went to the actual customer service reps across the hall, but we got them as well)
One day a customer calls wondering why we changed per payment due date. This is not something we could do (or that could be done) easily. At the time a customer’s due date was determined by the first number on the credit card- 1 is the first, second or third; 2 is the fourth, fifth or sixth, etc. This woman’s account number started with a 9 and the due date had always been the 30th of the month; but this month her bill said it was due on the 28th and she wanted to know why we had changed it.
I was baffled. I assured her we don’t go around changing peoples’ due dates at random. She was very polite, but very confused about this. (so was I) I asked her to hold for a moment while I looked into it.
The evening manager was not available so I asked a couple of my coworkers if they had ever heard of such a thing happening; they all replied they hadn’t. After exhausting all reasonable paths to try and figure out what the hell was going on, I was about to get back on the phone and tell this poor woman I had no idea why we had changed her due date.
Then it hit me.
I got back on the phone and said, “Ma’am, I know why your due date changed from the 30th to the 28th. It’s February. It will go back to the 30th next month.”
She laughed and apologized for taking my time and that she felt silly for not figuring it out on her own.
I apologized for not realizing it sooner myself.
TL;DR- Customer and I both forget February has only 28 days.