My girlfriend's ex is stalking her online

So.. this will prob take some explaining and im bad at explaining things, but ill try. So my girlfriend's ex has been stalking her tumblr (just about everything im gonna say we have evidence of), visiting it just about every day since they broke up (more than a month). Not only does he visit the page every day, but he has openly admitted to going there for the purpose of finding embarrassing things for him and his friends lo laugh at. I feel really bad because she hates it and there doesnt seem to be anything i can do about it. Ive already told him to stop and so has she, but we are met with an extremely aggressive response which is essentially him saying "dont tell me what i can and cant do". anyone have any advice?