They hacked my server

I've been receiving repeated attacks for 2 days now, somehow a hacker is abusing some exploit and changing his own UUID within my server and managing to delete the entire server, I've already created a system to prevent him from being able to have the UUID of another player other than his own and also being able to put an OP or * permission for himself, it even worked in the first tests, he was being banned, until he managed to bypass it again, I disabled the /lp and /op command for everyone, but it still continues, and the worst of all is that it doesn't generate LOGs, because the Hacker somehow erases the entire server, the only thing I noticed was him changing the UUID several times during a short period of time, my Proxy is Offline. Server 1.16.5, java 11, velocity, ambassador