While You Wait for the Truck
Close the main shut-off first. If you cannot find it or it will not turn, the curb stop near the street can shut the supply, though it may need a special key. Then go to the breaker panel, but only if you can reach it without standing in water.
Water on the floor plus energized outlets is the hazard that hurts people on these calls. If water is touching outlets, cords or a power strip, stay out of that room and tell the dispatcher. Get papers, medications and valuables up and off the floor.
Dispatcher tip: Tenant with a landlord who is not answering? Close the valve, photograph everything, and send a timestamped text and email so it is clear you moved fast.