Firstly, gotsomenow, never buy pc worlds components, not for the obvious reasons that are mentioned above, but basically because they are over priced and out dated, there are a great many places where these items can be sourced cheaper online. If you need any pointers I, (and i'm sure all the people here) will gladly give you any help you need.
My story, first I've had dealings with the Dixon group before and when it comes to returns they are the worst, like the OP I should have known better.
I live and work in Dublin and my aunt asked me to buy a pc for her family for christmas, (joys of being an IT graduate) I chose to buy it from the PC World website for two reasons:
1. There is a PC World beside her so if anything went wrong she could go there, I'm not home too often and honestly get sick to my teeth having to fix pc's for everyone who knows my name when I get home.
2. It was actually good value!
I ordered it in mid Oct (lots of time for christmas right?) well the cash was charged to my credit card rapidly but by the end of November there was still no sign of the pc, a full month after it was due to arrive, PC World where not answering my phone calls, the one in Blanchardstown is the only store that can handle online sales......I asked my aunt to ring them from her home phone and they answered quickly. She didn't really know what to ask so we didn't get any really answers, we weren't expecting them to answer seeing as they weren't answering to me, I never thought a company that large would screen calls.
In a fury I drove over to PC World in Blanchards town and immediately asked to see the manager, I let him know in no uncertain terms that I was not happy and that I knew they where screening my calls. He denied this, so I asked him if he had his mobile on him, he did so I asked him (while we stood in the middle of the store) if I rang would anyone answer and if they did not answer in a reasonable amount of time if he would then ring the same number from his phone to see if they'd answer it. He sheepishly said that would not be necessary, all but admitting I was right. He assured me that the pc had been specially shipped from England, I asked for the tracking numbers. It emerged that they had been shipped the previous day (from blanch) they arrived at my aunts house later that week. But they had delivered a CRT monitor not the flat screen I had ordered.
I was furious, I picked up the entire pc and brought it into blanch, plonked it down in the middle of the floor and demanded that they sort it there and then or give me my money back. They spluttered around, firstly denying that the pc I bought came with an LCD, I asked them to check it online to back up my claim but they had no internet access to check the offer online (believe that if you will) when I showed them a print out of the web page (I'm a quick learner

and made sure I went in prepaired) listing the offer they changed their tack.
They final got me a 17" LCD, I asked it I could see it working before I left the store, they said they had no where to plug it in! I pointed at the PC displayed 2 ft away from us and asked how about there? I plugged it in and found it was littered with dead pixels so I asked for another one, after a lot of rolled eyes and huffing they got me one which turned out to be good.
I haven't stepped back in there since.
You need to be really firm with them, not agressive or shouting obviously, but let them know that you know your rights (dates and names of laws scare the crap out of them) and what you are talking about technically.
Good Luck OP, but personally I wouldn't go to the S.C.C. just yet, go back in there and don't take no for an answer.