PNA Lost a customer forever

I am appalled by the service I got from PNA Lydenburg Mpumalanga. On Saturday I went to Nelspruit to do monthly shopping. I happend to purchase for over R500 at PNA Crossings in Nelspruit. I bought art journalling supplies. One of the pens I bought, is dry. I can't use it. I wanted to exchange for a new one, as I really wanted the pen for doodling as it is waterproof. The owner of the pathetic PNA shop, said she can't help me, I must go back to Nelspruit to exchange. Her system doesn't allow her to exchange anything bought at another PNA shop. I have my receipt for the pen. I have read the terms and conditions on exchange, and nowhere it says I must go back to the original shop. It only suggests it, but it's not a condition. I now can't get to Nelspruit before the 10 days are over in which I am allowed to exchange, and on top of that it will cost me R400 in diesel to get there for a pen worth R40. I tried to contact PNA on their FB page, they only read, no reply. This is how they treat customers. Lydenburg PNA is never stocked up, it's an excuse of a stationary shop, especially the art department. That is why I need to drive to Nelspruit for my supplies But a pen.... a simple pen... Thank you for not taking your customers seriously. I will pass on the word.