Log book declaration

Has anyone else had this issue?

I bought a car in August and had a lot of trouble getting the log book from the previous owner. It eventually ended up with me in late November making a declaration of ownership of the car (signed by peace commissioner etc) and eventually I got the log book in the post last week. Now, since I got the car in August it has been in a garage for a couple of months and then parked up, but even though I got the log book last week I have been put down on the log book as the owner since August so now I have to pay back tax to tax it. So, in August when I bought the car I had no log book to tax the car and had no log book so I couldn't declare it off the road either. So it seems the new law doesn't legislate for the position I have found myself in. Both local tax office and Shannon have said there is nothing they can do for me.