If you paid any part of the money by credit card, you'll have to make two separate claims. You claim against the credit card company for the money that was paid using their card and you claim against the CAA (under the ATOL scheme) for the remainder of the money (excluding things which are not covered by them, such as travel insurance premiums). The CAA will not refund monies which were paid by credit card.
Credit card companies usually refund monies within a few weeks (although there may be delays if lots of XL customers all claim at once) but, with around a quarter of a million people affected by the collapse of Britain's third largest tour operator, it's likely to be many months before most people get their money back.
To get to the head of the queue, print out and complete this form (and get it in the post as soon as possible):
http://www.caa.co.uk/XLLeisureGroup/Really_Gre at_Holidays_Claim_Form.pdf
Chris