This one I think. Ebay PC. The seller makes no mention of a Dell disk in fact he says "For Windows 7 Premium add £79.00 Genuine with Disk and COA Installed." Which is a reasonable price for windows 7 though you could have bought it cheaper from Dabs Outlet on Ebay.
Did you pay the extra for Windows 7 if so you have not got what you paid for and I doubt the legality of sending you a Dell disk for what is not a Dell PC.
In the first instance I would get in touch with the seller and point out you paid for a genuine Windows 7 disk, which you did not get, find out why Linx was on it and not Windows 7. I am assuming you bought the Windows 7 from the same seller as the PC?