Stay out of the water. Sewage is Category 3 black water, loaded with bacteria and pathogens, and wading through it or attacking it with a shop vac is a genuine health risk, not an overcautious warning. Keep kids and pets upstairs, stop running any water in the house because every flush and load of laundry feeds the backup, and if the water is near outlets or the panel, kill power to the basement before anyone goes down. Photograph from the stairs for your claim.
Then hand it off. This is the one loss category where DIY is simply off the table. Nonstop Restoration extracts the sewage, removes contaminated porous materials, disinfects and sanitizes, dries the structure to prevent mold, and documents it all for insurance. If you carry the sewer backup endorsement, this is exactly what it exists for. Any hour: (403) 620-8489.