Got a reply already - that was quick! And they didn't even try to tell me I was wrong!
"Dear Maryann,
Thank you for contacting Audible. My name is Nika and I'm here to help.
I am sorry if you didn't receive your $10 coupon. No worries, I can definitely assist you on how you can get your $10 coupon on your account.
Upon checking your account, I found that you have purchased 4 books within the November month.
As a valued customer of Audible, I've already issued the $10 coupon on your account. You can now use this for purchasing any audiobooks on Audible.com within the range of $10.
Thank you for taking the time to reach and inform us about your concern. Remember that we value you and your business with Audible."