Check the contract, receipt, estimate, "on and off contact" letters, emails, or notes of phone calls, and anything else in writing from the shop, as well as their displayed policies, and see what they can claim you agreed to. If there's nothing, then they can't.
But 3 years is a long time, and obviously a history about this, so I suspect there's more to this story then this 2 line query. See your own business litigator for help.
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