Service center returned my technical with no oil in the engine

I have take my bakkie in for service. I was charged for fluid change and what ever else the service included. Was told that everything as been checked and sorted. I am not a mechanical person and I don't understand the inner workings of a car. I awesome the agent knew what was best and had given me what I paid for.

Yesterday morning when I filled fuel, I ask the attendant to checking the water level of widow washer. While doing this he also checked the oil level. He informed me that there was no oil in my engine. I then check it twice. The oil stick came out dry. Too my horror I watched him fill 4 bottles of oil into my engine before the oil stick indicated the correct level.

HOW CAN THE AGENT REMOVE THE OLD OIL AND NOT TOP IT UP WITH NEW OIL!