Amazon South Africa "loses" purchase data to avoid payment of returned goods postage

I purchased printer cartridges advertised as compatible in HP printers costing R599. They were not compatible so I requsted a return of the goods and a refund. Amazon agreed to this and sent me a Return Mailing Label with instructions to send the goods back to the seller. The instructions from Amazon stated "the return postage would be added to your refund". I couriered the goods to the seller as a have good reason to distrust the Post Office, After some delay the seller did refund the R599, but did not refund the courier fees. I did bring this to the attention of Amazon but had no response and no refund. After about a month I looked at my Amazon account to query the lack of response. Now, I could find now trace of the purchase tofollow up my query, only thing shown was a product I never purchased. I eventually found a Customer Service chat facility and despite giving the agent the Amazon Order number, and the Return Mailing code, he said he was unable to trace my returned goods order. Amazon have conveniently "lost" the information so I have no recourse to claim the promised return cost.