Did you reconfigure your Norton firewall, as well as changing listening port?

Try a different port in that range that LOTR gave you earlier. Are you using LW during Tiscali's peak hours (6pm to 11pm Monday to Friday, and 12pm to 4pm on weekends and bank holidays)? Have you tried connecting outside of peak hours?

If you'd like to try port forwarding, the instructions for your router are here: Port Forwarding for the Siemens GigasetSE587

You'll need to set up a static IP address first & that info is here: PortForward.com - Free Help Setting up Your Router or Firewall

LW's listening port, port in the 'manual port forward' box & port forwarded within the router all have to be the same number