in parkour i helped a guy at lvl 2 and when i made it i pressed the sign to lvl 3 i was lvl 8 good it get lvl 8 again proof;https://gyazo.com/16f5f2378deccd450cea7c485a16c97a
Email [email protected] with the proof you provided and tell them your problem. But it might take a week to get a response so I'd recommend just trying to re-do the parkour.
I don't think you can have problems fixed for you that you made the mistake of doing. It would be like if I went to survival and I accidently through my full enchant sword into lava and wrote a support help about it saying I accidently through it into lava and want it back. Though maybe the owner will be nice enough to give you it back if you email at [email protected] with proof of you being on level 8.
You made a mistake by yourself, its not the servers fault so you will have to go and get back to the level you were. And why is it so hard to get to the level if you made it once already?