I just got the same email. But I have been sending out codes and it's part of my marketing, so it is a hit for me.
However, I'd never do anything fraudulent. I do pretty well with audibles and I wouldn't risk that. I don't even know how you'd use them fraudulently. Not the new ones anyway. I've never heard of them being sold.
They did seem to give me an extra hint at what the issue might be in my case by adding this sentence in: "Going forward, please also make sure that you observe ACX’s guidelines (http://audible-acx.custhelp.com/app/answers/detail/a_id/8887). "
I have recently published a collection of novellas, which included a novella that I'd previously produced on its own. I didn't realize that this breached their codes of conduct as I've seen people talk here about publishing boxsets on audible and how you should wait until the sales of our book slow down before combining them because it will affect the single books' sales. I've written to them in reply telling them I didn't realize this based on what I'd thought of as general knowledge in the author world and normal practice for eBooks and paperbacks. I told them I'm happy to take the book down now that I know, but just want to confirm it all. If it is this, why wouldn't you just write and say that this novella is included in this other novella, please take it down?
I've got lots of codes out there through sheer hard work and marketing, and I haven't used any other platform to distribute them. I'd copied some onto a spreadsheet for ease of use to distribute them, and I've only just sent some out in the last forty-eight hours, so I don't know if those will be redeemable or they are canceled as well. They don't mention any of that.
I'm wondering if this has anything at all to do with the expiring codes, which expired on the 9th. I sent out an email to my mailing list offering these, especially to UK people because I hadn't used any. So, I've recently had a lot of codes redeemed. However, they told us to do that in the email advising us they were expiring.
It's very distressing but if I don't get a good reply, which from reading here, I probably won't, then I'll use the Jeff Bezos email and persist with it. I need those codes for reviews on my books and my launching strategy.
I haven't had anything like this happen before. It's very upsetting, for sure.