caught a guy filming me in the gym (19F)

I’ve just left the gym slightly shook because I was on the abductor machine and I caught this guy staring at me, I stop until he looked away and finished my set until I saw him with his phone pointed right at me and he was looking around as if that would make it less obvious. I had to be sure so when he was doing his set I walked past and did indeed see myself on his phone including a video of me earlier doing another exercise. Feeling very violated right now. I think he looked under 18 but I’m not sure, with the New Year’s resolutions there’s been an influx of teenage boys in my gym and it’s made the space slightly less welcoming. I’m not sure I know his face because it was kinda generic so I’m not really sure what to do now.

EDIT: I’ve reported it and the gym is going to look back at the CCTV footage to figure out who it was