Spar Supermarket Clayville Mall Of Tembisa

On Saturday of the 31st I bought a coffee at Spar Supermarket Clayville/ Mall of Tembisa. The coffee I bought is Douwe Egberts and I looked for contents of the coffee at the store before purchasing. It did not show any information that it has caffeine so I bought thinking it's decaffeinated. I started to realize yesterday on the 2nd of January that the coffee has caffeine. I went to the store where I bought it today and asked the store supervisor if they can refund or exchange but the lady told me that it's impossible since I have used it. I am requesting help as a consumer because I used the coffee for only 3 days and caffeine makes me sick I cannot continue drinking it. I asked for refund or exchange for something lighter but they are refusing. I am stuck with a coffee that I will never take again. And I think it would not hurt for the store to take the coffee back to the supplier and explain the customer's reasons but they choose not to assist me. I am asking for your intervention.