Pathetic service at Waltons in Hatfield

A few days ago (22 March 2018) I went into the Bidvest Waltons store in Hatfield to purchase toner for my Canon Pixma MP510. Since I had never bought the toner before, I asked the lady to assist me by giving me the toner that would be suitable for my printer. She proceeded to hand me two toners (one color and one black). Much to my surprise, when I got home i realized that she had handed me the incorrect toner. The only thing to do was to take it back, I could not instantly take it back because I stay in Boksburg and the store is in Hatfield.

However, today (27/03/2018) I finally managed to go back to Hatfiled to exchange the toner fro the correct one. When I got there, the lady (who I assume is the manager) told me she cannot exchange it for me as I had opened it. She advised that this is head office policy. I asked her for an email address of someone I can contact at head office, she did not give me this, she instead went to the back office and came back to show me my slip that said "We will gladly refund or exchange any item in a saleable condition" according to this manager, the toners were not in a saleable condition as I had opened the box and plastic containing the toner, but the seal on the toner was not broken. I have no problem with this clause, but my issue is, how was I going to be able to see that the toner is incorrect if I did not tear the box? How is it that I am being punished for the mistake the sales lady made? This is absolutely crazy and a crime of sorts surely.