I'll give this a shot...
WWYD? I would first find a way to remove the published piece of work or indicate somehow that it is still unfinished work. I would then ascertain what piece of evidence it was that negated my hypothesis. How does it conflict with previous results? Is it the only time this particular outcome has presented? If so, why? Was it an issue with instrumentation or method? Who was performing these tests? I would say that if there was no evidence of anyone trying to manipulate the data or malfunction in the apparatus used or mistakes in method, then I would redirect the discussion to why the hypothesis was in invalid. Yes, it may be disheartening to have hours of work go down the drain but it may still inspire future research.
I would also address the issue of the supervisor publishing my work without consent, in a non-confrontational manner. What was their motive? Did they think they were doing me a favour by getting the research out there or were they trying to sabotage my career? Should they have known better to ask for consent? In either case, I would encourage them to speak to appropriate authority about the misconduct because it is still intellectual property that they published without my knowledge - regardless of if they were my supervisor or not. Now, they may not take lightly to this and so I would do my best to make them understand that I am looking out for academic integrity and trying to understand why they felt the need to publish the unfinished paper.
I may still attend the conference, seeing as it is in a month. If the time and resources permit, I would perform another round of testing (if I didn't conduct the last confirmatory tests in the first place) to ensure that the hypothesis is in fact invalidated. It would be degrading, in a way, to have such an outcome but I would be transparent about the results. It would be unethical to publish false claims, so I'd make the presentation about why or where it went wrong, and discuss the original purpose of the research had the hypothesis been valid. Definitely would highlight the importance of having protocol or procedures to prevent things like that from happening to other research teams.
There would be issues of use of resources and funding essentially 'going to waste', as well as the time of the research team (and test subjects, if they were part of the research) if the hypothesis was indeed invalid. I'm not certain what the procedures would but as a form of courtesy I would apologise for using up their time.
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Not really sure about the ins and outs, but I've tried to explore as many facets of the case as I could think of and the issue of academic integrity at the forefront of my answer. Feel free to add your own thoughts!