Change of assessment on land value

Has anyone had any problem lately, with the value assessed by the Land dept. on land purchase? I have just received a note from my broker, informing me that (just now, a full year after we originally filed) the Land Dept. almost DOUBLED the value of the land I purchased, and require an additional almost 4K USD in "stamp duty" to register the purchase.
Anyone has had a similar problem? I'm inclined to fight the valuation.
Does anyone know of the mechanism to fight that, and/or any lawyers specialized in that?
I feel that this is extortion. I won't go down without a fight.

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