FTP / HTTP to a NAS from the outside world

[#1]

I have a Netgear NAS duo hooked up to a Belkin Model No. F5D9630-4 with a fixed IP from Plusnet.
I have created a shared folder that I need to FTP / HTTP to from the outside world. Access to this folder is read only and write restricted to only user names as set under Manage users.
The problem I’m having is that from the outside world this share folder is not seen. FTP access has been set up on both the NAS and under Firewall Virtual Servers on my router. I have as a test disabled Firewall and NAT within my router and I still can’t gain access.
Can anyone advise me where I’m going wrong and what security measures I need to take when it comes to opening ports.

[#2]

Can you forward the port to a computer to test if it's an issue with the NAS? That might be restricting access to internal IP's only.

[#3]

FWIW some routers make a hash of exposing a FTP server. The reason is simple, in "Classic" FTP the server initiates the data connection, which often fails if the client is behind NAT, but should work with the server behind NAT. In "Passive" FTP the client initiates the data connection, which is difficult to make work when the server is behind a firewall as the data port number is not predictable. A "DMZ" connection should work though.
Years ago I had a Linkstation visible via FTP but it required a substantial block of forwarded ports to get round the problem.
Incidentally its worth checking if the NAS server has a gateway configured. If it doesn't it'll be visible locally only.

[#4]

Oh and if its an option HTTP is a lot easier to forward.