Paying because of their faulty system

I am very disappointed with Jet. I bought a pair of boots from Jet Maponya mall for R299.95 on the 10th of May 2019. On 11th of May 2019 I returned them to Jet Dobsonville. I was told that the amount was going to be refunded to my Edcon account but upon getting my statement on June, the amount did not display on my statement. I contacted the Edcon customer service who also failed to locate the funds and even failed to facilitate communication with the store involved. On the 8th of July I went to the Dobsonville store and they promised to contact me as soon as the matter is attended to but until today they have not contacted me. My concern is that I paid for goods that I did not use and as it is an account purchase, I continue to be charged interest for something I did not use.