Hello,
I get where you are coming from. This is pretty common among the audiophile community. I keep all of the original stuff that came with the stuff I buy. If it was important to you it should have been a question for the seller. That being said I would download the manuals and read what the amp came with. Also, If I was the seller I would have comped you for the cables some how. To start with what to do is ask the seller for them which you did. If you want these amps do not go any further with returning or filing a claim. What I would do is call a Bel Canto dealer and see if they have the original pc in stock. You would be surprised how many black 14 ga cables they have in stock or they throw away. I know this is not ideal, but let it go. If you don’t then you probably just wanted to return the amps regardless of the PC. Again you are talking to someone who loves to keep all original stuff with a purchased product but in the end you made a communication mistake and the seller assumed something. Please let it go for 15 pounds. It is not worth the stress and time you are wasting on this.