Does customer communication (answer) following a complaint is a mandatory requirement per FDA or MDD. Can it be concluded from ISO 13485:2016, SEC. 7.2.3 (C) : "The organization shall plan and document arrangements for communicating with customers in relation to customer feedback, including complaints" ? or perhaps this paragraph is intended to state that as part of the complaint process we need to communicate with the customer in order to receive as much as possible adequate information and data related to the complaint event.
It is a mandatory requirement to inform the customers of the complaint if it is pertaining to a medical device recall or a field safety corrective action as the customers might need to quarantine any stocks that have been sold out or are currently in their warehouse. You should be looking at clause 8.2.2 Complaint handling which provides you with more information on the procedure of complaint handling. With regards to clause 7.2.3, it means that the company should have a way to get feedback from a custom er with regards to the purchased product or services (quality or not quality related), including complaints.