It may not be very helpful at this stage, but I normally photograph packets that I assemble and send, in various stages of "dress"... mainly to avoid the "it wasn't packed properly" problem.
I suspect it's up to Scan to "prove" the CPU wasn't in the package. I'd contact Consumer Direct in the first instance, collect advice, and I'd then send a polite and detailed letter by registered post. Explain that the two were in the same package, and describe the packing. Give them a set time to respond (but be generous, say 21 days, maybe).
I've had a bit of experience with returns to Scan, and it was a bit chaotic sometimes (e.g., fault with TV/remote; shown to be remote in home testing, sent both back, Scan sent on to manufacturer, manufacturer confirmed remote faulty, but didn't return remote to Scan, phonecall 2 months later from Scan, asking if I still had the remote!)
Patience and politeness should see you right. Being a non-ranter is always the best route