Welcome to the forum Lee, you'll find the members on here are a friendly and helpful bunch :)
The c5 a6 is a great car. Is there not a way you can find out if it's taxed, like you can in the UK?
Also it might be worth you posting on the Audi c5 group and just Audi Avants (,I'm assuming yours was an avant) on Facebook.
Cheers
Steve