As title states, my rank was removed after my name change. I sent some sort of support ticket or something, but I'm not sure how I went about it. This happened years ago when Mojang introduced the ability for everyone to be able to change their name. My previous names were vMpee, vaMpeex and Fledge if that helps. From memory, vMpee was the name I donated to get the rank for. Surprisingly my brother regained his rank after his name change, mine did not.
I'm not searching through years and years of transaction receipts just for this, I'm sure they have vMpee on their records of donors.
Not too sure if they can search by your username. However do you have your rank on any of the gamemodes?