Port forwarding on Thomson TG585v7 ......... help please!

[#1]

I have the supplied tg585v7, a while ago I fitted an IP camera and forwarded port 81, all worked fine from anywhere and via Dyndns.com.
Removed the camera and fitted another on port 99, deleted the old "game" info and did a new one the same for port 99 [and since moved the camera back to port 81 also]. No success what so ever, all appears to be there on the router interface but no forwarding happens.
I have redone it several times, soft reboot, hard reboot, factory reset and now software update to 8.2.6.5, still no go! The camera works fine if accessed internally [192.168.1.99:99].
I have blindly played with Telnet and done a save all, no go. Is there a Telnet command to set a particular port to forward as it's all a bit of a mystery to me at the moment and as for the CLI guide, it seems to have everything other than port forwarding?
Yes I've been to portforward.com and that's exactly what I have been doing/did, it worked here originally and is still ok on my 585v8 at home.
Could anyone please offer some words of guidance before I get out the 5lb lump hammer and ask Plusnet for a new 585v8 as an insurance claim! What is the obvious thing that I am missing?
One last totally unrelated point, can your IP [dynamic] address be changed by your ISP without the line dropping out, I didn't think it could but mine seems to change occasionally without any visible signs?
Thanks, Bob.

[#2]

Hi there,
With regard to the port forwarding, it might be worth factory resetting the router to default settings before setting up the port(s) to be forwarded? As I understand it it should just work using the router's pages, you shouldn't need to use the CLI.
As for the IP address, that will only change if your connection to us drops and is resumed so all I can guess is that there are very short drops in connection causing the changes. There's not many disconnections showing on the account linked to your forum profile though, is that the one you mean?

[#3]

Hi Matt,
Thanks for the reply you've beaten me to it, I was just about to sit down and write the following.
Last night I had one last go [whilst looking for my 5lb hammer] and went through and did everything again going back to the original port 99 [not for the first time], deleted/checked camera settings, deleted/checked dyndns settings, deleted forwarding in the router and did it all again [with my eyes shut by now], nothing I hadn't done before [allegedly] and behold it worked instantly, sorry, I have no idea what was different this time!!
Yes I had done a router factory reset but that was some time before and it made no difference.
I might add that the router web interface works quite a bit faster with the latest sofware installed, it's now only just mildly annoying.
The IP changes were on my line at home [user name with a 3 on the end], it was just something I noticed had happened once the other day, it doesn't matter at all and as you are pushing the line to work rather hard for me [and it's absolutely fine thank you] I think it must be left well alone please!
Both my accounts are running on the ragged edge of what Mr BT will allow us to do [thank you lots for this] and any disconnections are usually down to me fiddling about after a 1db night time drop out etc, I'm really happy exactly as I am thanks!!!!
Regards, Bob.
Apologies for the underlining but I wanted to make sure you didn't adjust my account in any way, this is a very happy sleeping dog.

[#4]

No worries - I didn't touch anything and will be sure not to, don't worry!
Glad you got it sorted though, weird how these things can suddenly start working even though nothing different has been done.

[#5]

Thanks Matt, it was just that the thought of hearing those words again:
"Return to square one and when you get there ................Please plug into the test socket and report back" ............. is enough to bring on a case of the shakes again!!
I think it's more a case of even though "you think" nothing different has been done, "faulty operator" it's called in my business [and probably yours]!
Have a good weekend.
Cheers, Bob.