Purchase Contract Validity

My father signed a contract to purchase a hearing aid for $389.00 with no deposit required. The contract did not specify what portion of the contract was for fitting and ear impression. It only indicated the total price of the hearing aid. My father passed away before he had a chance to pick up the hearing aid and never took possession of it. My mother received a bill (addressed to my father) for the $389. We called the seller and they told us that we are liable for $130 for fitting, etc. Is my mother liable for this amount?

No because mother is not a party to the contract.

In addition to HomeGuru's correct response, I add the following:

The your mother is not personally liable for the debt, your fathers estate would be liable for it.