I know what you're saying as you can be fined for not having a valid tax disc displaying, even if you have paid, and even if as in this case it's the DVLAs fault. I'm not sure that taking the car off the road would even work though, as a SORN declaration hasn't been made. In which case if they don't sort it then I'm guessing that the only way round it, annoying as it would be, would be to have to pay the tax AGAIN and then try to claim it back.