Shocking customer service

I am shocked by the customer service (or lack there of) by Fedex. On the 11th November 2023 the driver delivered my parcel and by accident overcharged me almost R1500 (he had the wrong customer invoice on hand). After numerous mails with all the relevant information like bank confirmation letter, bank statement, ID, invoices etc. still nobody could achieve in solving the matter and refunding me. My mails just keep on being forwarded from one person to another. I struggle to understand how such a reputable company handle issues like these so badly, and having a look on Hellopeter to see how many other customers have the same issues are even more shocking. I would love for someone to assist me or at least just communicate regarding this.