Now that the ACA covers older dependents, what happens when one misses a payment?

Q: The ACA covers dependents up to age 26. They are classified as dependents under the provisions of the medical plan of which their parent is a participant. In our employee's case, a son was 21 at the time that medical treatment was provided. He has failed to pay the deductible for treatment under the plan to the provider. As a result, the medical provider is billing the dependent’s parent and threatening to put the issue into collections and take legal action. The question is, who is responsible for the deductible payment? The dependent here is not declared as a dependent for income tax purposes. – Terry, New Jersey