Frustrated Customer

Hyundai SA is the worst auto dealer in SA. I have my car for 1 year now and not once did I receive an aftersale call. My car went for a 15000km service but at 20 000km I get a display message telling me it's due for a service. When I contacted them, I received one stupid email telling me that the service intervals are 15 000km, like I don't know that. My question was and still is WHY AM I GETTING A MESSAGE NOW, 5000KM LATER, REMINDING ME ABOUT A SERVICE AND STILL NO ANSWER