Should you have paid their price by use of credit bank card, there may be another
proof of purchase that a store management personnel may consider adequate.
Another question comes to mind, in that had those earphones been damaged and
returned by a different retail buyer, and not set aside, they may have been already
some other's warranty replacement file. As such, they shouldn't have been re-sold.
Once some years ago I bought a portable music player from big box store in Seattle
and gave it to a friend as gift; on opening to set up the unit, found the batteries has
already been installed. I also found an older 'dated sales' receipt in box. It was used.
And receipt of first retail buyer had paid less new, than I did, for used/new product.
The manager not only got it back, also received tutorial on their lax return screening.
Then had the manager look into the sealed retail carton of replacement to see if that
one had been a return, too; or not. I insisted. And had them test it as well.
Hopefully you had separate proof of spending the money there, with the correct
amount in the records. For cables to be in 'failed-state' from new box, is wrong.
A copy of credit card billing date, if bought by that means; or challenge the bill if
bought on a bank card. ~ Cite unfitness of merchantabilty, or misrepresentation?
Receipts and other paper proofs (serial numbers, etc) can be helpful later, even if
the item isn't problematic; original packing has important info on there, too.
Good luck & happy trails! 🙂