Sorry, there's no 50% rate. If the house has remained furnished while it has had no occupier, you should have been paying 90% of the full Council Tax throughout the whole period. If it's unfurnished, you were not required to pay Council Tax for the first 6 months but you should have been paying the FULL Council Tax after 6 months.
From my local council's website:
"If a property you own becomes unoccupied you must tell staff in the Council Tax department immediately. You could qualify for a reduction if the property is unfurnished. For six months from the date the property becomes unfurnished, there is no tax payable, provided the property remains unfurnished and is not lived in. After that, full Council Tax is payable. The person responsible for paying is the owner or the person who holds a lease or rental agreement. If at any time during the six months the property becomes occupied or furnished, you must tell us immediately".
Source:
http://www.midsuffolk...scountsAllowances.htm
And from where I used to live:
http://www.sheffield....-your-bill/empty-home
Chris