How old is your home? Are you on a slab or pier and beam? Do you know if your sewage and water/waste system is Cast Iron or PVC?
The reason for my questions is that this same thing happened to us. Our home is 30 years old, on a slab, with cast iron pipes.
Cast iron pipes begin to decompose around the time frame of 30-35 years. At that time, the bottom of the pipe just rusts away and the ground becomes the bottom of the pipe. Dirt, roots, and debris begins to block the path and you have this problem.
We had a complete pipe re route done. It was all done via tunneling. We had our entire pipe system replaced. During the investigation process, they removed our commode and sent down a minny camera. The camera was connected to a monitor and we saw what we could not believe. Many of our pipes were like an inverted "U". They had no bottoms.
This test can be done very inexpensively and your insurance should take care of it. Be ready for a major home renovation. If we ever had to do this again, we would just sell and move "as is".