Where is Dell's customer service?

Hi,

I bought a Dell XPS630 in October, I had to order via phone as online wouldn't let me have the TV tuner and the dual graphics card. I spoke to Waris and he took my order, I upgraded on a few things including the processor from Q9400 to Q9450 (£100).

I was promised an email that day confirming my order and all I needed to do was reply and the order would be placed. I received no email, I called 2 days later and was told my PC was on its way. Great I thought and the PC arrived but when my invoice arrived it showed that the processor was the Q9400.

Since the 24th October I have called, left messages and been promised a call back, I have emailed my account manager and his manager and used the unresolved issue option on this website. But no one has got back to me at all!

I find it amazing that a company like Dell has no interest in keeping new customers happy.

Does anyone know how I can complain and actually get a response?

Thanks