Name Change, Locked Out of Chests

[RantosSymphony]

Hello.

So a while ago I joined this server as XIII_Derp, some time passed, I changed my Minecraft username, and now I'm back. The chests I claimed while still using the name XIII_Derp are now locked to me. Could I get any help with this problem, I'm not too sure what to do. My username is RantosSymphony and the coordinates of the chests are X: -5585 Y:63 Z: -14766. The chests in question are on either side of the coordinates.

Please and thank you!

[mjw8441]

All done, seeing as you weren't on at the time I've changed it to your current username rather than just breaking the sign