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Presumably you have done work to your property.  If so you were asking for trouble if you tried to reaccatasto the house as an a3 - economic typical housing.  An A7 is a villetta or upscale rural property.  Now you can ask for a check - ultimatley catastal values are down to a bloke and how he feels on the day, but they are also down to the information given by your professional when you when signed off on the work you did,  If he was a little economical with the truth. you could be in for penalties.   He tried to get in under the wire as an a/3 and they looked on google and decided it was an a/7.  It all depends on how mch of a stink you want to raise.

We have rates here on a small Island  for properties and if there is an extension or works carried out to add to the value they can re-evaluate the rateable value.  This is what worries me in Italy.  Have you had any major works done?  We had our Italian house painted outside in Italy and works inside, I am waiting for mine to come but I have a feeling we are A7, I hope so.   We pay nearly €2,000 per year for our house in IMUs and then everything else on top, it’s quite an amount.  I hope you can sort this ok, we think we may have to sell when we retire as this amount of money just won’t be there each year.