F’ing Septic Tanks

Have you checked all commodes or other places that may be running all the time? Just a commode that is leaking through will fill the tank up. If you have a water meter check the dial on it and see if the arrow is moving when everything is off. If that is not the problem see if drainage is good around the septic tank and field lines. With all the rain we have had this season the water table is way up. Maybe the county inspector can tell you what type system was installed. If it doesn't have chambers and you need to upgrade field lines that would be my suggestion