Not updating the address on your V5C is a separate offence, but not one that you have been charged with.
Broadly speaking, a notice delivered to your "last known address" is lawfully served on you. You still have the right to make a stat. dec. as the right to a fair trial includes the right to be heard, regardless of the fact that the reason that you were not aware of the proceedings was your own fault, and a separate criminal offence.
Whilst you do not appear to have a defence, resetting the clock to the trial would enable you to enter a guilty plea (for which you could get up to 1/3 discount off the fine), potentially reduced costs, and negate the subsequently escalated recovery costs.