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I am sorry to learn about this doubling in price for your home improvement contract. Unfortunately Massachusetts (while being one of the more protective states for consumers) does not have a statutory limitation on how much a project can exceed the initial estimate by.
However, if the contractor performed the work before they got your permission to proceed at the increased price, they cannot enforce the new cost. (in which case you could consider a small claims case for breach of contract to settle the dispute)
But, if the contractor let you know that the cost was going to be higher (even if it was in the morning when they were getting ready to start work), and you agreed to the increased expense, then they can hold you responsible for the new amount.
(That doesn't mean you cannot try to negotiate something with them, many businesses work on a basis of trying to keep positive consumer reviews and similar public relations goals, so they may be willing to adjust their position out of recognition that their statements to you were misleading at best).
You can try filing a claim with the BBB: https://www.bbb.org/consumer-complaints/file-a-complaint/get-started in both cases - the BBB acts as a mediation service of sorts for consumer disputes and is free to consumers to utilize. They have no enforcement powers, but for minor disputes such as this, they can be effective (particularly since all BBB disputes become part of the public BBB ranking for the business)