I am sorry to hear that you had this problem with PCW. I too had issues with them, once I had brought an Advent PC from them, but these were resolved once I got annoyed with the sales staff trying to fob me off and asked to speak to a Manager or go to Trading Standards.
You will probably not be surprised to know that the consumer magazine Which? rated them as one of the worst for customer service. It may be worth dropping them an email detailing what you have told us, as I believe you at least should have a written apology from the regional Manager of PCW at the very least.
Thankyou for letting us know about this, I am sure there are some people, who are not that well versed with the Sale of Goods Act, and good easily be bullied into walking away from this situation; so I applaud you for seeing it through.
All the best and I hope you don't have any more issues with your machine.