Your system is different than ours. We do not have dampers in the fuel lines. We also have check/roller over valves in the fuel tank to prevent fuel from leaking out the gasoline tank should the car be inverted in an accident or over filing the tank.
One possibly reason you can not put fuel in the tank is because your canister is full of gasoline and thus there is no way for air to vent out as you displace the air in the gasoline tank with fuel when refueling. Remove the canister, start the car. If you do not get a puddle of gas forming from a leak, drive the car to nearest filling station and try to put additional fuel ( just a few gallons, don't completely fill it) and see if that works: Yes, then check valves in the filler neck are ok; No, then trouble internal to to the filler neck check valves.
REPLACE THE GAS CAP WITH A NEW ONE WITH THE SAME PART NUMBER AS THAT WHICH IS ON THE CAR NOW! No excuse, just replace it with the exact same part number.
Try to get a new unused canister as a replacement or a used one which has not been soaked in gasoline. You can reuse the one you have if you thoroughly dry it out, but it will not have the capacity, nor work as well as a new one.
If you find a small value in the vent line that runs from the canister back to the fuel tank (small white plastic?) get the part number on it and get a new one. It is a two way pressure relief valve. If it is stuck because of dirt from the canister and it probably will be, as the dirt flushed into the value from the saturated canister.
You say you have a good shut off valve on the canister per your test. I'm not convinced of that, but it's your call.
Good Luck!