Stores refuses to credit my delivery money

I ordered furniture from this store and paid over 3 months, the sales person who assisted me was Lunga Mtiya who recently resigned from the store. I was asked to pay R500.00 for the delivery of the furniture which I paid cash to Lunga at the store, which he noted and signed for on my purchase order. I later decided I was going to collect the furniture myself from Rochester Warehouse in Jetpark, so I requested Lunga to PROCESS a credit for the R500 delivery fee, which he sent me a credit request form to fill in and told me it takes about a week to process at the head office. A week went and no correspondence from anyone, I then went to there to inquire, the store manager told me Lunga was on leave and will be back the following monday. I explained to the manager my predicament and she looked into the matter & found that the was receipt done for my payment. she then said she will ask Lunga when he's back from leave where he recorded the payment, on that following monday I phoned the store and they told me Lunga had tendered his resignation over the weekend with immediate effect. So now they don't want to pay me back, instead telling me to chase after Lunga and get him to pay me back.