Originally Posted by
mstateglfr
Just return it and see when a size S will be back in stock. If it's a reasonable time, wait.
Companies aren't perfect because people make mistakes from time to time.
Once a bank (or, more accurately, its ATM) made a mistake in my favor. But a more realistic (cynical) interpretation is that they sold something they didn't have, so they did a substitution with the hope that the buyer wouldn't care, or wouldn't make a fuss out of it.