I'm really sorry it happened to you. My last apartment was full of black mold, and probably had been for at least a decade. It was a nice place to live, but we were constantly getting terrible coughs, sinus infections, and sore throats that improved once we moved to a newer home.
You will absolutely need to throw out the bedding. Black mold is a killer. And it thrives no matter how much you paint over it, spray it, or wash in bleach. Walmart has cheap blankets and sheets these days.
Cut into a small patch in the undersides of the mattresses. And check the walls behind dressers/bedframes/shelves. It's most likely there too.
In the future, vent the rooms, and use moisture absorbers.
It is also very important to keep furniture off of the walls. Let there be about 2 to 3 inches airspace between any piece of furniture and a wall.
Inside the home, it is the tenants job to prevent mold overgrowth. If they see it, the tenant must do all they can to remove it. And if it's not removable off walls by washing, they report it to the landlord for repair of any structural defects, and for the landlord to paint over mold on the walls/windowsills, or replace caulking or grout. But in most cases, it's the tenant's fault due to creating humid conditions and neglecting upkeep.
Also, saving up and investing in a dehumidifier would improve your life so very much. Until then, run fans after showering or cooking, and vent the windows as much as you can.