Shoprite signet terrace does not work as a cashtill

This has happened more then once. I have a fnb account and we allowed to draw money fromthe tills but always when I go shoprite tillers do not have the money, the recent date is the 23 December due to the inconvenience I had to go to the atm tiller why is shoprite said to give money but shoprite signet does not have the money available constantly...