fuck man im replaying alpha sapphire and i have my 7th badge. I just got Dive and now I am at Sea Mauville, grinding these rematches with these spooky sisters for a 5% chance at a dawn stone

I have the rematch available, and I saved right in front of them. I battle them, win, dont get anything, so I immediately soft reset. Apparently this can be done to get more chances at this dawn stone

but dude I have grinded this out for a total 6 hours now, and have easily done this battle more than 50 times and i have not gotten a dawn stone. Am I really just that unlucky or what am i doing wrong