Netstar's Incompetence and Unjust Harassment Over Paid Contract

My brother bought a car from Hyundai Strijdom for cash in December 2023, and we also paid R5,879.83 for a 3-year contract with Netstar. However, Netstar has not acknowledged the payment and continues to demand additional money. Despite multiple attempts to resolve the issue with them, they refuse to address the matter with Hyundai Strijdom. Eventually, they escalated the issue to their creditors department.