FTP Port Forwarding Issue

I have a friend for whom I am setting up FTP so that he can access home files when travelling with a laptop. The particular FTP combination is:

Netgear DG834Gv2 Router
DLink DNS-313 FTP Server
ISP Pipex
DynDNS

This is a situation I have set up successfully several times, albeit not with this specific combination of router and ISP. So far as I am aware the settings are all correct. The FTP server is configured correctly (I use the DLink DNS-313 myself) and the router has Port 21 forwarded to the LAN static IP of the DLink (192.168.0.10), and DynDNS works for me (albeit with O2). Yet Port 21 remains closed and I cannot access the FTP from outside the LAN. Indeed I don't seem to have control over any ports except Port 80. Although I am familiar with several Netgear Routers my immediate thoughts were that I had made some basic setting error. But I have tried everything I can think of, including enabling/disabling NAT, enabling/disbling DMZ, dipensing with firewalls altogether etc. I have even tried upgrading/downgrading through the last 5 firmware versions for the router. No effect whatsoever. I am beginning to wonder if Pipex has blocked just about everything, but I have not asked as talking to ISP help lines is generally bad for my blood pressure! So far as Netgear is concerned, there is no reason why port forwarding should not work with a DG834Gv2 even though it is quite an ancient router - but of course they could be wrong!

Does anyone have any ideas please?

if you enable logging on the firewall page does it show it rejecting connecitons ?

have you tried using the prevailing WAN IP rather than the dyndns lookup ?

Pipex is now part of TalkTalk, so there is a good chance inbound FTP may be blocked. I don't know for certain though.
You could try changing the port on the FTP server to something else (also changing the port forwarding rule within the router to match) to see if the problem remains.

Or if the router is capable of PAT, map a different inbound port to port 21, then try connecting via the port number you used.

Very many thanks for both replies - great help, and there's always something fairly obvious that I don't think of! On your excellent suggestion I have now reconfigured both router and server to Port 1030 and FTP is now fine. It seems that Pipex/Talk Talk/Tiscali or whoever they are now must indeed be blocking Port 21. Many thanks again for the help.