I'd say the waste line is plugged between the house and the main. Call a plumber.
I wonder if you could set off some tannerite down there somehow? That'll clean it all out.
The worst toilet adventure was a downstairs toilet that would flush perfectly two, three times and then the forth flush
would have you doing the shit water tapdance. Then it would flush fine again. Snaked it multiple times. Pulled the toilet twice.
Re-educated the entire family on how you don't have to make an "oven mitt" of toilet paper to wipe your butt. I covered all the bases.
Could not figure out for the life of me why the water kept backing up every once in a while.
Until I discovered, after pulling the toilet for a third investigation that a Welshes jelly jar lid will act like a
butterfly valve and wont simply fall out of the removed toilet. It has to be pushed back out the way it came in.
Damn toddlers.