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The ftp server we use is on port 21, I don't have a static IP. POrt 21 is the industry standard. Your service provider is out of step.
You would have to get your service provider to set the port. Like that's gonna happen.
Port 25 is usually only used for smtp, like they say using it for ftp will invoke the same rules as set up in their firewall for smtp.
I'd change my service provider.

How do you mean set the port Mick?

TCP services use ports set on the server, you can configure these in any way you like as long as the port number is not in use by any other service. Something of the order of 6.5 k ports available. There are industry standard port numbers used for various functions. In your case your provider has set up their server to use port 25 for both smtp and ftp. This allows them to set just one set of rules in their firewall, instead of configuring the firewall to protect two separate open ports.
This will give you some background in FW protection of a server. http://infopeople.org/resources/securit ... figuration

I'm still confused a bit! If I access a companies ftp that they have set up to upload a file, then I could previously using port 21. However setting up my server at work opening port 21, then accessing from home didn't work, yet I could the company's even though I was using port 21. Now I have a static IP I can do both. How come on a dynamic IP I couldn't access work but could the other company? If anything was blocked it would be the same port for everyone?

You can access any ftp server regardless of port number, as long as you know what it is from any IP static or dynamic IP? That would always be the case.
You'll need someone a lot more conversant with this than I to explain why you need a static IP to access your own server. I was thinking you were using O2's ftp servers. The only thing I can think of off the top of my head is that when at work you're on the same NAT addresses and when accessing externally you have to go via port 25 as the address you want to go to is ftp://xxx therefore their system does not recognise the address unless it is concluded with :25 once routed to your office the port number may be ignored and just the ftp://xxx part is used. Providing their firewall doesn't block transit Hence the static IP.
This is just conjecture on my part as I haven't tried it.