I got caught out by the catcha, it's case sensitive, managed to do it on the 2nd attempt, I think there is an option to have a spoken letter, maybe try that.
EDIT, I just checked and if you click on the speaker symbol you can hear the numbers. Although I don't know why I'm telling you this, after the less people who can the competition the more chance I have of winning.....lol.
Good luck..
Rog.