Horrible customer service

On 21 October 2022, I purchased the prescribed medicine from the Dis-Chem store in Stellenbosch Square and was overcharged by R899.55. I went back to the store two days later to have them rectify the mistake. I was told that they don't give out cash and could either give me a shopping voucher for the same amount or try to refund me via EFT, which they discouraged based on the likelihood of receiving the funds. Before agreeing to accept a shopping voucher I asked the cashier if I could use it when making a purchase online, to which she answered yes. On 30 October 2022, I tried to use the voucher to check out online, and it failed. I went to the Dis-Chem in Sitari to enquire about the issue and was told that the shopping voucher could not be used for online shopping. Furthermore, I was initially told that I was supposed to be given back cash for a refund for being overcharged. This back-and-forth experience has inconvenienced me as a customer.