I have had the same increase in my Fonciere and Habitation. I have been told that because I have work done (septic tank, replacement windows and new electrics) that I am back on the Radar and they have increased all the taxes in line with current values. You may notice that the rentable value has increased by the same percent and this is the base value for calculating the tax.
The house was owned by an elderly French couple before and they probably declared no changes to property in the 70 years they owned it. I did complete an assessment form sent by the tax office.
I am happy to pay my way but I feel a bit stupid for being so up front. Although this is probably what most etrangers would do.