I had occasion to ring them twice recently with queries not answered clearly anywhere on their website. I found them very helpful, but be careful- accents were foreign on both calls, so be ready with clear questions, and ask them to repeat answers if you dont get the accent at first.
If you look up the list of registered properties on the website, you will --well, you MAY --find your property registered, though they said this has not been updated from last May.
The registration and E70 fee is (sort-of) attached to the new tenants, so if you have the same tenants for up to 4 years you do not have to re-register, only initially.
My problem was that my tenants had no PPS numbers, or would not give them to me-- ((and I dont see why I have to try and prize this personal information out of them anyway??? )) They returned the form and cheque to me, etc--- but on phone they advised me to write a note to that effect, and re-send it.