Long story short, I bought an SD card for my phone. It has a 5 year warranty in the usual terms - replace with similar or better, or full refund, at their discretion. A couple of weeks ago it became faulty so I returned it. It was packaged with an adapter I never needed or used, like this (but 64 not 128):
I got an email back saying "what about the adapter", which I don't have, and was a very minor part of the product.
I'm sure legally that they must honour the warranty, but I'm at a loss how to best demonstrate that's the legal position, or that I don't need to return the adapter to claim in full on the warranty of the card itself. The item is too low value to be worth getting legal advice (about £30)
What is my position, and what would some helpful relevant legal arguments or UK consumer law precedents be, to research it or avoid a long dispute?