Force upgrade not working

Hey Roman its me, the guy you changed the server software from forge to spigot.... But there is another problem...
First time when i start the server after you changed the software and when i joined the server my friend houses are gone and mine too and also other stuff, but the world is the same. Then i remembered there is a force upgrade button and i shut down my server and opened it again with force upgrade ON and i go in console and there i can see loading chunks, loading nether , loading end (we had a nether portal and end too before you changed it back to forge) I dont know what to do ? It says its loading the old world but its still the same without our houses stuff creations and other... What should i do Roman ?

Thanks

Yeah but in the console it say the world is loading and also nether and end world

Sorry then i was thinking the force upgrade button was for uploading your world in the server.
But look nevermind the force upgrade... When i upload my old world why doesnt it load into my server