Unhappy Client

I received a courtesy car which was extended for extra 3 days after 30 days authorised by Miway and now im getting calls from a collections company sent by Avis demanding payment of R1500.00 and ive been in contact with Miway asking different consultants to resolve this issue and i was told by Seipati Ngake from Miway in September 2018 that they are waiting for Avis to send them an invoice so that Miway can settle this amount... to this day im still getting calls from Credit works demanding payment from me... each and everytime i call Miway im told the matter has been escalated to car hire department to resolve with Avis and they will get back to me... but none of the consultants have never returned any of my calls... the only email i received from Seipati was an email to Avis and that was because i requested that she forward it to me... Im not happy and this is frustrating