While you've been given lots of good advice, try other sites, shoot until they take it etc. all of which is valid to a degree.
Id also encourage you don't let it get to you and always approach it with the best attitude and expectations possible.
GIve the benefit of the doubt, accept even if you did hit them, it might have hit a pouch or the adrenaline etc meant it wasn't reacted to in the time you could see them. Be the best example of an airsofter possible, when hit shout things like "cracking shot!" Etc. everyone who has played has not taken hits, they've hit pouches, running around while weak shots come in etc. at the very least something has obscured their view of you before you've been able to react, leading them to assume you're cheating
Every time I hear about poor hit taking, it always seems to get worse, only positivity about sportsmanship, great play, great hit taking and the power of embracing the game has ever turned it around on the day.
Also, make sure your kit is in order. I had it at my last game, I popped a corner, shot at 2 guys and only 1 took it (cue the "wtf you cheating cu*t" look at him)....at my respawn I realised my gun wasn't firing due to a jammed BB in the mag. Never happened before and I run a gun that stops firing with an empty mag(not a gbbr) so when it fires, it fires. I've done over 5000bbs and not had a single jam in this gun so for it to happen then, in that scenario was....annoying.
I've also had my rif just seemingly power down during the day, 1.1 joule at the start of the day, 0.6 at the end and all during it I thought people weren't taking their hits....worst day ever for cheating etc. Actually, I either wasn't hitting them or the shots were so weak they couldn't have been felt.
Fundamentally it happens, intentional or not and it's something that happens in this imperfect game based on honesty. Yes, do what you can to minimise it, attend good sites, be a beacon of a good airsofter, have yourself and gear in order. If you can't deal with that, I'd suggest switching hobbies.