Really disappointed not going the extra mile

I received a gift and wanted to exchange it for another gift as it was something I am not very fond of. I explained to the customer service desk agent she wad helpfull but then when I eventually chose another gift and was about to do the exchange they said they are unable as they were unsure if it was bought on the 3 for 2 deal. I left very dissappointed and paid for my child's goggles and hand soap which I was going to exchange for the gift I received. Then a few minutes later I went back and requested the store manager and they called the assistant store manager. He asked if they helped me and I said yes. Then he also said they can't assist me... very dissappointed in that as I have been supporting this dischem since they opened in the mall more than 9 years ago. It is Christmas time honestly. Never ever complained about their service and always spend more than R1900 every single month there. It could've taken then just 5 mins to put a smile on someone's face for Christmas... all this just for R140.