We recently sent a notice of intent to file to a non paying customer. They have since hired an attorney and have sent extremely threatening emails, accusing we are in breach of contract, asking for full reimburesement of the project amount. They also state since we didn't provide notice of right to cancel on the agreement, they are entitled to a full refund.
It probably makes sense to hire an attorney at this point. Though, hiring an attorney depends on the amount owed by the (I presume) homeowner. Sometimes the amount is small enough where it does not make sense to hire an attorney. Though in this case, with an attorney involved, it makes sense to hire an attorney.
The attorney in question appears to be referencing the right to cancel inherent in Ohio's Home Solicitation Sales Act (HSSA). While it is true that your contract likely should have contained this language, the right to cancel only lasts three days from the date of the contract. From the way this message sounds, many more than three days have passed. Absent the HSSA right to cancel, the homeowner does not get some unilateral right to cancel the contract on a whim. Additionally, even if the homeowner could cancel the contract, the cancellation does not cancel your right to be paid for work performed.
You should speak with an attorney sooner rather than later.