Final answer:
The next step would be to send a letter of formal withdrawal to the patient by certified mail.
Step-by-step explanation:
The next step in this process would be to send a letter of formal withdrawal to the patient by certified mail. This is necessary to communicate to the patient that they will no longer be treated by the practice due to their refusal to comply with prescribed medical advice or treatment plan. It serves as an official notification and ensures proper documentation of the decision.