I was a victim of the Snapchat blackmail and I have no idea what to do now

Hi, yes I have also been a victim of snap chat blackmailing scam where we swapped nude pictures yet the other side was fake and have naked vulnerable pictures of me and they are now threatening to post them on my IG and to my dad. Others say to just block them and nothing will happen, but they have sent a video to my father so I believe they are not playing around and this information will go round to literally everyone. I really value your time and would really appreciate any advice that you would be willing to offer.