Whilst I can appreciate your problems and frustration I feel that you really have left it a little too late in trying to get any sort of satisfaction from Dabs.
Yes, Ok the CPU was DOA but you have, albeit through no fault of yours, left it too long.
They did eventually offer to replace the CPU in September, some 8 months ago. As you state, there is a 1 year warranty and that you have not returned it within that time your own statement would seem to apply -
"I argued that I could not be held responsible if their website acknowledged my form submissions but they did not receive the same on their back-end data systems or failed to act on it"
In other words, why should they now be held responsible if they have given you an RMA number eight months ago and you have failed to act on it? (Granted, you have very justifiable reasons for not doing so, but there is little in the way of sympathy in the dog eat dog world of commerce)
Put it down to experience and buy another CPU. They will no longer be able to replace it anyway and as they have already stated, you are out of luck on the refund. AMD will not be interested as the warranty has now expired and any cynic would probably say that this is an attempt to get an upgraded CPU for free!
Sorry, but I do feel that action as soon as the RMA arrived would have been your best bet.