Wow. That must have been a hell of a breakup if the only thing they want to say to their ex is simply ‘No’. Better not to insist. It’s time to move on.
Sending your ex (or anyone for that matter) unwanted nude pictures is never the way to approach them. No one enjoys getting a nude they didn’t ask for. This shows that guy is their ex for a reason. Blocking and reporting that kind of people is the best course of action.