no service tag - no support

I have been unable to get support over the phone for my 2408wfp, which is now displaying red and green vertical lines. Twice I have been told that if my monitor lacks a service tag, then it must have been purchased from a fraudulent retailer, which is nonsense, since I purchased it from Dell directly. I informed the service reps that I could provide my customer number, order number, and the monitor's serial number. Despite this, I was told that without a service tag number, no warranty assistance would be offered.