I would write a very calm but detailed trip adviser review for each one. Highlight the good, but give complete details of the incidents of being overcharged. Hotels read the reviews and if they see a sane person who obviously isn't flying off the deep end when writing a review, it will put them on notice, unless they just don't care. You might also want to fire off some polite nasty-grams to the corporate HQs if they are chain hotels.