Amazon Customer Service Can't Fix USB Mix-Up , I Got 64 GB Instead of 256

I recently bought a 256 GB USB stick from Amazon.com.tr, but when I got it, I saw that they sent me a 64 GB version instead. When I called customer service, they told me that the website's system made a mistake in the title about how much space the USB had. They told me that they would refund the price difference if I bought a new one of the same brand from the same seller that was the right size. I trusted their advice and went ahead and made the extra purchase as they suggested. But when I went back to customer service to get the refund they said they would give me, they unexpectedly said no. The way things are right now makes me angry and annoyed. I want a fair way to fix this mistake and keep the promise that Amazon.com.tr customer service made.