I am one that paid twice and will eventually receive a credit for the duplicate as per my conversation with Janis.
Here's the thing though, because of all the glitches with registration I have spoken with other people that were in the same position and received the same letter. The problem ties in with the fact that some regions reported having received more entries than the 750 cutoff. As a result, if they decided not to pay again to get the site to recognize their entries being paid, many other people did and once the 750 paid entries were recognized their payments were not allowed and basically they got shut out
Don't shoot the messenger, this is only what I am hearing from those I know that this happened to-I'm sure it will get worked out:)