How to fight with mold on wall and ceiling connection on last floor
Depending on where you live and the rights as a renter, this seems like something that should be taken up with the building owner. You can certainly attempt mitigation, but from personal and anecdotal experience, mold growth that shows up in living areas, is usually a sign of much worse mold behind those visible surfaces.

Often times this would require mold mitigation up to and including removal of interior drywall/plaster, removal and treatment of mold growing on the internals of the structure, added ventilation and treatment of the problems causing mold growth, and the reinstallation of mold/mildew resistant materials.

This sounds like a bigger job than just removing the superficial presence.

Remember, just because you cannot see the mold, does not mean that it is not affecting your health or your property

I encourage you to take this seriously and have this issue corrected.