Bank Robbery and teller-Riddle

Jagga is robbing a bank and he tells one of the tellers to give him all of the money. The teller tells him she doesn't have access to it. Suddenly the phone rings. The robber tells the teller to answer it and not give them away. She picks up the phone and it happens to be her mother. She tells her mother "Is this an emergency mom? Call me when I get home, I could use some help painting." Then she hangs up.The robbers continue to try to get into the vault but twenty minutes later Detective Mehul shows up with the teller?s mom and arrests them all. How did he know about the robbery?