Do you have anything in writing about the promise to repair the mold, or what was meant by "repair"? Your landlord may have thought it enough to seal the mold behind new paint.

Usually it would be pretty obvious if a more significant repair than a coat of paint were performed. If drywall were removed, there will often be a visible change in the appearance or texture of the replaced material (particularly in a $400/month apartment, where the repair would be done "on the cheap), and the trim would be replaced, or would likely show signs of having been removed and reattached.

You should consider getting a mold testing kit to see what mold spores are present, and if there's any sign of toxic mold.