Such a thoughtful gift for your parents turns into a nightmare! The attitude you found from Celberity is unspeakable, considering the push that they (and several other cruise lines) make to push bon voyage gifts on their websites.
I'm glad your story had a happy ending in that your parents were able to redeem (through their own dilligence) your lovely gift. But shame on Celebrity for the shocking treatment you received in a post-cruise follow up. I would follow up that little conversation with a nice letter to the CEO that included the representative's name and a transcript of your conversation with him/her.
Sorry to hear it was Celebrity; I've had nothing but raves to say for them based on my own experience.
Another vein: You should join your parents on a cruise! I am taking my 85 yr. old mother on Constellation in a few weeks. I regret that I never did this while my dad was alive, since he was a great deal of fun. But I'm grateful I can do it for my mom, since she hasn't travelled in several years and would never do so alone.