A3s of that era were prone to failure of the instrument cluster which gave similar symptoms to your car, so it is possible your A6 suffers in the same way. Audi will want a small fortune for a new cluster in England or a large fortune in Norway. The clusters can be repaired at much lower cost if you can find a suitable company. If you can not find a local company it would be worth investigating if ECU Testing, a company we often recommend here, would do it.