Don't pay them anything, I had a similar issue, said a vehicle I had sold was recorded as being parked on the road and clamped. (the camera vans). Wanted me to pay £80. Wrote them a letter explaining I had sold the vehicle and that they should now hav3e updated their records. They sent a letter back basically saying no, you're the registered keeper. I ignored the next two letters, then received 6 pages of court paperwork. Last page was only a print out of the registered keeper I sold it to. Alsp stating the date of sale 4 months previous. That boiled my piss. Wrote them a snotty letter stating that they are obviously a bit thick to see the registered keeper doesnt match my name or address and even slightly thicker not realising that the car was clamped outside the registered keepers address. They wrote me an apology stating to ignore any future correspondence. If you've sorned the vehicle on line you should have an email or print out of when you sorned it, and if/when you get the log book it will state one you became the registered keeper, so you should have evidence if they try and pursue you for 2 years worth of sorn. Other than that tax it the old fashioned way, down the post office