Most of us reading this are probably saying to ourselves "just turn up the heel DIN bro", but giving advice on safety equipment over the internet based off one sentence of context isn't a great look, so instead its probably better to just say general advice on DINs:
1.) Check forward pressure or other adjustments (looking at you, Salomon bindings with a ton of adjustments). That could be cause. Check for excessive wear on your boots, this could also contribute. If you are still concerned the binding simply isn't releasing correctly, (not DIN to low, but DIN is set reasonably and it feels too low/high) you should be able to take your skis and boots to a ski shop and test it. Sometimes older bindings test lower than they are set, or in the case of Marker the other way around (I had an old griffon set to DIN 8 test at DIN 9).
2.) If you are still having pre-ejection issues, you can turn up your DIN but obviously you need to understand and accept the higher risk of injury, namely tib/fib fractures but also to a lesser extent other injuries. People argue over whether your DINS need to match or not, my personal view is that mismatched Heel/Toe DINs sound weird but there's no real reason to crank your toe DIN if you're having heel ejection issues. Whether you match them or not, you only need to turn up your DINs to the point of them being skiable, no need to max them for the sake of maxing them. If it doesn't give you any issues at DIN 8 don't crank it to 12.
3.) To prevent ACL injury, best you can do is get your legs strong, do your stretches, and learn about what types of falls to avoid (phantom foot and slip-catch). Muscle fatigue is also an injury factor so maybe curb trying a new trick you're likely to fall on late in the day when your legs are toast. Unfortunately modern ski bindings do not really protect your ACL well, and Pivots aren't an exception. I think If I remember correctly, some of Rick Howell's research suggests an average adult male can still tear an ACL at DIN 4.
