Wrong memory in computer

I am having big problems with my computer and HUGE problems with Dell "Support" (ha, ha, ha) and in an attempt to see what is going on in said computer I downloaded Fresh Diagnose which shows that I have 512MB memory installed. When I bought the computer in January I bought it because of the special offer of "Memory: FREE UPGRADE! 1GB for the price of 512MB" - I am quoting from my Order Confirmation Am I misunderstanding something or did Dell send me less memory than they said they had in the hopes I wouldn't notice (which I didn't for 7-8 months). Incidentally I live in the Caribbean where we constantly find we are sent second rate stuff (everything from lettuce to fridges to cars) because it is so hard to send the stuff back. Why else would things be labelled "For Export Only"?, but I'm getting off the point.

I am pretty good at using a computer but know very little of the workings of them - what does everyone else think and what do you all think I should do? Also see my messages under this board of 27th September and under General - Non Technical dated 28th September and today to see how hopeless everything seems.