You clean the shower, but the mold comes back. Mold grows where surfaces stay wet for a long time. Poor airflow, damaged grout, and water leaks can all cause this. Soap residue and body oils also feed mold. Wet towels and bath mats can keep parts of the bathroom damp between showers.
Cleaning the mold you can see is often not enough. Good airflow is one of the best ways to stop mold. A mold expert says to turn on the fan before or when your shower begins. Keep it on for 20 to 30 minutes afterward. Leave the shower door partly open, and hang up wet towels. Does mold keep returning to the same place? Then ask a professional to check for hidden leaks.