Given that I have the memory of a goldfish that would be my fear as well......
Apart from that catching the perpetrator in the act is usually the best fix but seeing its happening in the night.....and I'm getting a solid 3-4 hours sleep a night....
Disciplining one of them is out of the question unless I know the one responsible. Did that before and found one was doing the damage to watch the other one get a smack....until the one making the mess got the wife's bra caught in her collar while emptying the dresser....
I guess since keeping the paper in the vanity for a week or two or closing the door when not in use are the next steps. being locked out -- hey wait --- maybe locked IN would be better.......

One of the BEST ways to discipline both cats and dogs?
When you catch them in the act? Yawn, BIG YAWN, and look away. As in fully turn your back & ignore them.
It works better with dogs, than cats, but it’s a mammalian cross species shunning gesture similar to human dropped shoulders and head and saying “I’m not mad, I am just so …disappointed…. In you. And ashamed, and will need some time before you don’t make me sick to look at you.”
It’s also why we know when cats are mad at us, when we leave for too long. The deliberate turned back, and refusal to look at us. Until they’ve forgiven us.
Cross species body language doesn’t always translate, and there are things (like yawning, instead of poor posture) that one finds amongst 4 feets but not 2 feets (and vice versa)… but the yawn & turned back? Is a vey effective one to turn on 4 feets. Because it’s only done to creatures you LOVE, not enemies. So it’s a 2 part thing, conveying both love & disappointment.
If you’re SUPER pissed off at a cat, and want them to know it, AFTER yawning and turning your back… IF they come close to apologise (9/10 they do, to beg your forgiveness) hiss and swipe your hand at them. Don’t actually hit them/touch them, their mom wouldn’t -though siblings do- just make the gesture, and turn back around. It is extremely rare that they will ever repeat the thing you’re pissed off about. But save it for extremely special circumstance. Or you end up with an extremely phobic/anxiety ridden cat.