Along with plenty of others following this thread, I ordered a games controller on line (£99.99) from Savvibuy with the express promise of delivery before Xmas. Identical experience to others - e: mails promising guaranteed delivery before Xmas, apologies for delays etc, etc.
I informed my bank (NatWest) who asked me to complete a form and send to their "retailer dispute team". Because I had paid via a debit card I thought I was never going to see any money, but I was informed that as Visa is on my card then there may be some protection. I can report that I have now received a full refund credited to my bank account by NatWest. Their letter does however say this is a temporary refund whilst they continue investigations on AdvanceTec. I think I am however confident that I will finally get the permanent refund. I have to say I am reasonably impressed with NatWest who appear to have taken the side of an "out of pocket" buyer. I will now check and double check the credentials of any on line retailer before I commit to an order.