@Yolojo The underlying root problem is that management has failed to install deadbolts or safety chains. That is clearly not your fault. The stuff about do-not-disturb signs, which call fall off of doors or be missing or get ignored, is a red herring: they often help but they are not reliable.
I think you could complain in a way clearly assigns blame to the hotel management, not to the cleaner, and I think that would be entirely justified and might also of service to future guests. You could specifically request that they install a safety chain or a deadbolt on the inside of the every room, in order to ensure the safety and dignity of hotel guests.
You could post the request as a public review, so that the management knows other guests will see your review and will know about the lack of safety locks unless they install them and then reply accordingly to your review. You could then send the review to the hotel manager to make sure they see it.
For example:
I felt unsafe in your hotel when I found myself alone in a room with an unknown man who had let himself in to my room at 8am.
It turned out that the man was one of your cleaners using the access provided by management, and he left quickly when asked to do that, but it gave me a real fright. Although he had knocked before entering, I did not hear anything because I was asleep in bed, and I was awoken only by the door opening and the man stepping inside my room. Any hotel really ought to have a safety chain or a deadbolt that when locked, ensures that the room cannot be opened by all of the cleaning and room servicing staff when a guest is sleeping inside. That will not only improve privacy and safety for your guests, but it will also reduce the risk of management becoming liable if you were to have bad luck and hire an individual who decides to commit an offense against one of your guests. Until this is remedied, as a female traveller, I would not choose to stay there again!
A review like that should only cause trouble for the cleaner if he is actually not supposed to be entering guest rooms at 8am, which is unfortunately also a real possibility! This is a bit long, but it is designed to make them see that while installing locks would cost a bit of money, not installing locks could cost them a lot more.