If you try to use the code on line, you will be asked for the last name of the person receiving the code, as well as their ZIP code. I planned and took a trip in Sept 2009 with my son for his 44th BD. All reservations were made through my email and I used both his and my own credit cards to make payments. Though BOTH our names were on the reservation, since it was his first visit I put his name first.
DH and I have been to WDW many times and have yet to receive a pin. However, I continue to receive pins every few months in my son's last name. So, go figure?
I have confirmed with WDW that, since this is my son and we did share the vacation, that I can book using the pin. None of the pins have matched our vacation plans yet, but I may put it to the test next year.
Do you have ANY idea who the person is whose name is attached to the pin? If not, someone may have given an incorrect email address so the offers have been directed to you.
I suggest you call/email the WDW corporate/executive offices and explain your frustration - that you continue to see a discount offered via your email that you cannot utilize, while you never receive any in your own name. Include the number of times you have visited and the date(s) you wish to plan for your next trip. You may be surprised what they can do and, at the very least, they should be able to remove the other persons name from your email address.
I learned many years ago never accept a "NO" from someone not empowered to give you a "YES" response. Even if you call the reservation number and get a regular CM, ask if they can grant your use of the pin number. When they say no, politely ask to speak to their supervisor. When you are transfered, ask them if THEY have authorization to grant
you a pin number. If they say no, listen to their reason/response, then ask politely to speak to THEIR supervisor or to be transferred to the Executive offices for assistance. (You get the idea, right?)
As for your "I'm not very good at sticking up for myself in situations like this" comment, you really won't have to be pushy or go beyond your own comfort limits, you merely have to ask - nicely -

. Persistance has its rewards.
WDW appreciates feedback - both positive and negative - that will help improve their customer relations. Their creed is made up of the words: Courtesy, Efficiency, Safety, Show, all of which have equal importance in the conduct of their business.
Now, put a smile in your voice and set your mind in "I'm going to help WDW" mode, then dial that number. Let us know what results you achieve!