Sorry about your problem. I would hope that you contacted the buyer first, so they would have a chance to straighten things out. That will clear up the problem almost all of the time. Failing any resolution with that, I would contact Mike Longo. I have found him very willing to make things right, for both sides. Don't think that your issue doesn't matter.
Feedback for seed sellers is a tricky issue. A buyer's normal response when receiving a packet of seeds is to leave feedback. That tells the seller that the package was delivered, and is the normal way things work. It is much more complicated with seed sales. First, did you get a reasonable germination rate? Most people don't plant their seeds right away, so there can be a considerable amount of time after the initial purchase. Secondly, do the seeds look like they are the correct cross? Now we're talking two or three years passed initial purchase, and you are way too far down the road for any reasonable resolution or refund.
Seed selling has always been a tricky area, and in the wrong hands, can be an easy place for fraud. Don't even get me started talking about when they used to offer pollen, or custom made seeds??!!
The only thing that gives me pause is not the 100% feedback, but the amount of feedback. I would think that fraudulent behavior would have knocked this buyer out long ago, which makes me more inclined to think error instead. Did they use new help, was there a mixup, a labeling error?? I would bet this is more the case, but I am only guessing at this point.
Let them know your disappointment and their response will tell you a lot. Never feel you are too small to take a problem to Mike if need be.