The employee, who did not want to be named, told the City Times she managed to alert her mother of the incident via a WhatsApp message from her cellphone.
Capt Alie van den Berg, of the Benoni SAPS task team, said four armed robbers entered the store at 1.15pm.
Victims were told to look down and lead to a backroom in the store.
The suspects stole money, airtime and cellphones.
The unsuspecting employee said she alerted her mother who then contacted Khosi Hlongwane, the Community Policing Forum (CPF) chairperson in Kingsway.
The CPF member then altered police.
Van den Berg said no arrests were made and the police are conducting an on-going investigation into the incident.
A case of business robbery has been opened.
No injuries were reported and no shots were fired.
In separate incidents, a butchery owner was robbed in Actonville on September 28.
A cash-in-transit heist was also committed at Lakeside Mall on the same day.
