Goods returned and never received my credit

I bought a Proline 752J 7'' WiFi Tablet 16GB - White <br> 752J for Christmas gift to my grandson. The tablet does not have a sim card slot as mentioned in the product description. I app**** for a exchange for credit on the 22nd Dec 2015. The parcel was picked up on the 30th Dec 2015 and delivered back to the warehouse of take a lot on the 31 Dec 2015 and received by Portia. Until now I havent received any credit for the returned product. Every day I phone and complain and then they promised to look into the matter and contact me. But no one ever contact me. I have a long list of names that promised they will sort it out but with no luck. I also used a R500 voucher that I need to be re-issued. Fed ex sent me a copy of the delivery note where the returned goods was signed for at Take a lot's warehouse.