Flight boost nightmare !!

I cant boost my flight because it says I have done Multi-city bookings , I did a return flight from Lenseria airport to Cape town international 18/04/2019 and I return on the 23/04/2019 . This is def not a multi city booking . I need this mess sorted asap , as I would like to get cash back on my flight . Vitality has ben nothing but a headache , if its not me constantly following you guys around to pay cash backs on races its this ?? why have a service that you cant run properly , I'm beyond disappointed .