SurveyInvitation + SurveySubject or Surveys. sendSurveyInvitationEmail ?

Hi there, 

I'm building an Apex batch for sending emails with link to surveys to the Contact in a Case. 

Is also required to relate the survey to the Case. 

To get that, in the batch class, I inserted the participants in the SurveyInvitation and after that, I inserted SurveySubject to relate the survey to the Case.

            SurveyInvitation invite = new SurveyInvitation();            invite.Name = param.CRM_Encuesta__c; // survey invitation name            invite.ParticipantId = c.ContactId;            invite.CommunityId = surveyCommunityId;            invite.OptionsAllowGuestUserResponse = false;            invite.SurveyId = surveyId;            invite.OwnerId = c.OwnerId;            invite.CRM_Case__c = c.Id;            invitations.add(invite);...            insert invitations;            // add Subjects to the invitations            List<SurveySubject> subjects = new List<SurveySubject>();            for (SurveyInvitation invite : invitations) {                SurveySubject subject = new SurveySubject();                subject.ParentId = invite.Id;                subject.SubjectId = invite.CRM_Case__c;                subject.Name = invite.Name;                subjects.add(subject);            }

However, nothing is sent to the contact's email.

I was told that I must use Surveys.sendSurveyInvitationEmail() method for sending the emails. However, using it, I see SurveyInvitation records it generates, but I have no way to relate them with SurveySubject records to associate them to respective Cases.

Any idea on how to solve it? Thanks in advance! 

@* Salesforce Developers *