I missed the date of my council tax summons

Other

I have an HMO, and in one of the units, croydon council got it into their heads that the place was empty for a period. so they sent me the bill. I wrote back with the tennants details, and they ignored me, and continued to send me the bill- with the 10% empty property discount. I replied to their letters at every stage. Then they summonsed me, i replied to the summons and they even acknowledged my reply to the summons, but i missed the court date- for the silly reason of absent mindedness. I would have won easily, I have the tennancy agreements etc etc etc- and also copies of all the stuff i sent to croydon telling them that i'm not responsible. I even have correspondence from Croydon telling me that my tennants are solely responsible for council tax for the periods that they live there.

but, now having the liability order against me, any ideas what i can do?