This code system http://hl7.org/fhir/communication-not-done-reason defines the following codes:

CodeDisplayDefinition
unknownUnknownThe communication was not done due to an unknown reason.
system-errorSystem ErrorThe communication was not done due to a system error.
invalid-phone-numberInvalid Phone NumberThe communication was not done due to an invalid phone number.
recipient-unavailableRecipient UnavailableThe communication was not done due to the recipient being unavailable.
family-objectionFamily ObjectionThe communication was not done due to a family objection.
patient-objectionPatient ObjectionThe communication was not done due to a patient objection.