The same thing happened with me too, I accepted a gift donation from PEDRO12 at the time I moved from a Tier 4 to a Tier 5 in late October last year. I was given the emblem when I moved to Tier 5.
The reason I didn't receive the emblem when I first became Supporter was because Toujours initially won it as a competition prize but transferred it to me as she already had Tier 5 Supporter on her. And it was my birthday too!