Hi, thanks for using JustAnswer.com I am Cris.
Did they have you de-register the Kindle and re-register back to your account?
OK, please try doing so. This will remove the Kindle from your account and may correct any glitches the device is having associated to your account. Once you have re-registered then you can re-download any books back to your device.
Let me know how this works out for you.
How did you make out?