GEMS Complaint

Was a member for a few years. Service was good and especially their walk-in offices where staff are friendly and informed. The problem that I have may not sound big to most people, but to me currently, it is. I had to resign from my government job because of family related reasons and therefore had to cancel my med aid as well. Long story short, after some time I got an email from GEMS informing me that they owe me R700 and they tried to deposit it into my bank account but couldn't. I responded that I have a new bank acc and included all the necessary details including my phone number. Received an email after that that I must phone them regarding this matter. I phoned, held on for couple of minutes before airtime ran out. Emailed them again, but no further response after that. Why must I phone and use half my airtime for money that belongs to me when I gave them my banking details already? Am I at fault here?