Make sure it’s not installed via the addons page. If it is, you need to click uninstall from there.
another thing to try, wait for your server to hibernate by having nobody in the server for 10 minutes, reactivate, set server to offline. Delete the jars while it’s offline, then start it up.
if none of my solutions work, you may need to open a support ticket and describe your issue: https://support.minehut.com/hc/en-us/requests/new