Toilet is not draining.?

If you pour an entire bucket of water in the bowl, does it drain quickly? If it does your flapper is probably fouled up, or your tank float needs adjusting to a higher water level.

Do you hear gurgling at the sink, or does water come into the sink when you flush? Your vent pipe to the roof might be blocked. Go up on the roof and check it anyway, even if you don't hear a gurgle at the sink...

Does it flush better after nobody has run water in the house for a while, like first thing in the morning? Your pipes may be clear but you may need to have the septic emptied. Also harsh chemicals may be killing the enzymes that break down the waste in the tank, causing sediment that prevents proper draining into the drain field.

Do you have little kids? Lots of plastic toys (perfectly sized plastic balls) get flushed that get trapped (float) in the air lock of the toilet- almost impossible to get out, and will cause the symptoms you have...

Good luck!

Call a plumber it might be something very simple, it might be a major error in the original construction causing an air blockage some where. It sound like you have tried all the obvious.

i was going to suggest a snake since its not a clog id consult a plumber