Refusing to Refund - Avis are ****mers!!!

I hired a Car at Avis on the 29th April 2025, I then paid the amount that was required and paid an extra amount for upsell. I returned the vehicle on the 13th May 2025. I have not received my refund back for the upsell amount till this day. I went to Centurion where I booked the vehicle and paid, they told me that it is their head office that does the refunds. I have been calling them since the 22nd May. They requested a proof of payment. I did that. Today Sandile Sehume is requesting my bank statement. They have taken me from pillar to post it is daylight *******. Please help