Minecraft Server

I changed my name to epicpvper because my regular name is MonuralPurse46 and it is a bad name so i changed it to evicpvper and i lost all my things and i could not change it back because MonuralPurse46 is a 14 character long and game is not allowing me to
go back.

How can I use my old name back as it had all the game play stuff I achieved and all my minecraft server things are gone.

So, please help me to change it back. Thanks.

:)