"Will they turn up at Small Claims Court?". Doesn't explain much, is it your intentions to proceed and do this!.
If you want any advice here, perhaps it would be better to explain the full details to the problem. Reading your comments, I could perhaps consider that the transaction was completed via the American website, in which case, you may have no claim against a UK company.
Who did you contact and ordered the CD from, and was this paid in £sterling or $US Dollars by credit card. How much did the CD cost.How did the original transaction commence for you to order the CD, because you state something about Winzip.
"Sent a recorded letter to the Manager", did you supply a direct managers name, because the company have stated that they have several, which I assume cover many different sections of the business.
Perhaps if you answer some of the above and make things a little clearer, then someone could offer further help and advice.