As Parsnips has said, its impossible to offer advice without knowing the approximate numbers. After all, 37% more than last year's assessment of (say) €100 is perfectly possible.
The same percentage on (say) €1000 would tend to suggest an incorrect submission of the numbers by you or an incorrect assessment by the Impots.
If you want to pursue this (which I'm sure you do), then pm either Parsnips or me with some details (I'm sure that I speak for him, otherwise he wouldn't have responded in the first place) and whichever one of us will try to help. Its private and not in the domain of the Forum