DELL Computers MISSING O/S DISC, Internet

I purchased a Dell Dimension pc in 2006 asked about O/S DISC--was told that it was preloaded--would not need a disc--low and behold now i need the disc--called to request one and asked was it normal for them not include this disc said it should have come with the pc-I have the purchase order with everything that was included--low and behold had to purchase the cd --sales reps were very rude --like oh well--very nice when i was purchasing the pc--I think they should have sent me the missing cd-only people i can contact is sell people no customer care people this is totally UNFAIR--CANNOT find a number to voice a complaint--think twice before purchasing a PC from Dell- they definitely will not be in my list on my next purchase