Not good news unfortunately - the following is copied from the customer services email:
Unfortunately my technical team have confirmed that the SIM card inside your device is faulty and cannot be re-activated.
As it is no longer possible to repair the Go 540 live model (there are no longer any spare parts being manufactured), the only option if you want to receive Live Traffic updates would be a replacement device.
We can offer you a 25% loyalty discount if you decide to purchase a replacement unit. Some of the new devices (eg. the Go 5000) now come with Free Lifetime Map and Traffic updates, so if it is a service you use frequently these added benefits may be economical for you.
If you do have any more queries or questions about new models please don't hesitate to contact me or one of my colleagues and we will be more than happy to help.