I was able to download all my bills except one: May 2015. This has been the case for months. When I click on May 2015, the following message appears: "Your bill seems to be taking a while to generate. Please try again later."
Thanks for your quick response! I am not on FB, and I just tried to send you a direct message on Twitter, but it turns out "You can only send messages to people who [follow you]": https://support.twitter.com/articles/14606