Orange are only responsible for the connection to your master socket. If you choose to connect to the router via wifi, that's entirely out of their control. You could try repositioning the aerial of the router and/or the wireless card in your PC. Some routers (my Linksys, for example) allow you increase the output power from within the configuration screen. You might also try changing the wireless channel of the router, as you may be suffering interference from another nearby radio source (such as your neighbour's router).