A grain is missing
Hades had been able to track down Natasha while avoiding a confrontation with Reaper leaving false energy signatures in multiple places. Sometimes even used living creatures and implemented his energy in them so that whenever Reapers sought him out he would be met with another creature.
That was his he had managed to stay alive up until after what he had done that Reaper marked him. As for Natasha, he could trace Reaper's energy in her and the souls of the dead people who were still within the soul ball. He could not claim them because Reaper hadn't given them to him but he could still use them to find the girl. After all, he was the god of the dead, and every sound in the ball was that of a dead human.