Yeah. This is sadly a common thing on parkour. Parkour does not support namechanges, but every other server does (Or staff can help with getting plots/islands back). Parkour ranks are saved on their names and not the player UUID. Until parkour gets a hard reset (Everything for everyone to 0), it won't support namechanges, but you can pay all your gems you have, to your new name before changing, if you know what you want to change it to. If you have any other question to parkour or in general, feel free to pm me on discord, ingame or here
Shron