We have received a new tax notice for our WoMo C 25, we should pay instead of 185,00 € now 460,00 € and for 2006 repayments. I have then with the tax office tel. and they informed me that I need an S 1 certificate, then it costs only 300,00 €. I have talked with Citroen and Hymer, they informed me that a particle filter only makes sense for the plaque, the price does not change. The installation of an Oxi-Kat costs with installation about 800,00 € and w Is there anyone else with good advice??