Believe your domain provider may be a little confused on what you are asking. You are not wanting to change your nameservers for your .org domain, just perform a redirect so that when someone hits the .org domain, it goes to your .net domain.
Most domain registrars allow you to redirect your domain to a different website. If yours doesn't, you're a little out of luck, I'm afraid. You would either need to point your A record to your own server where you can then do a redirect or find another solution. Unfortunately though, this is a little outside our scope of support as this is no longer our software or platform we're talking about.