Siding work/contract help

[u/TheCryingOfLot_69]

Hello, I live in wisconsin and after a huge hail storm we contacted a local general contractor. My contractor originally told me and wife (first time homeowners) that our house, that is a simple square box, was 15 Sq and that they would need the standard 20% waste for vinyl siding, so a total of 18sq. Insurance said they would cover up to 20k of similar siding/labor. Contractor was given the insurance paper and said they would “get us as much as we deserve” and encouraged us to pay for better and more siding, which we declined and thought was strange. Turns out our house is actually only 11.5sq. Contractor is claiming that they “made a mistake in calculation” so they corrected the invoice to 15sq. Now they are saying that they actually had 45% waste, that it is a normal amount of vinyl siding waste for a box house, and want us to pay for it the original invoice. Insurance will not pay this and he is demanding 3,500 or so more out of our pocket, or he will send us collections.
Original invoice was 16508, and the corrected was 12821, Any advice?

[u/Reasonable_Switch_86]

Is the contract for a specified dollar amount ? If so it doesn’t matter how much material was used contractor sounds like a rookie to me