Text output
Hi Dana, You ordered a medium and we sent you a large. That's on us, and I'm sorry you had to chase it. A medium is going out today by tracked post and should be with you by Thursday. You'll get the tracking number by email...
Reply to an angry customer without sounding like a bot
Paste the complaint and what really happened, and get a reply that deals with the problem in the first line, says what happens next and when, and skips the canned apology.