Nando's order missing a payed item.

Placed a bigish order from the drive-thru during lunch time today. ( ********** 8) Cashier goes over the order, everything I wanted is mentioned. Pay for the food, proceed to collect. I ask the lady is everything here. So replies, yes. I drive back to the office and a burger is missing. Now I'm let unsatisfied and at a loss because I payed for something I didn't receive. So, am I refunded for the burger or do I receive in-store credits?