Dell windows upgrade to windows 8

I ha for the upgradeve recently purchased DellI Ispiron 15 R SE ( 7520) withWindows 7. I have checked that I am fully eligible for the upgrade. But when I trued for the same I received the following message-

We are sorry.

Unfortunately, based on the information you provided during the registration process you are not eligible for the upgrade offer.

Please refer to the program requirements.

Your Reference ID: WU3864606727

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I have double checked the information submitted.

somebody please help.