Filling the gas tank, what can we eliminate

[lechCe]

Hi guys, I have a constant problem with the filling of the gas tank. Its 2000 2.7Boxster.
There were different threads on that issue, but hard to syncro the answers from them.

What goes wrong, and what I have tested:
-whenever I try to fill, it pops out as if the tank is full
-there is no smell of petrol in general
-there are no strange sucking noises

I have tested the small plastic tab next to the inlet, it doesnt change anything in my case. I also took out the bleeding valve that looks fine as operative. There is a magnetic sensor on it as I see? I guess this works fine.

I though of changing the vent valve which is just beside it, this will be my next step.

Looking at VIN specification I have the charcoal filter in my car, but I guess this would not cause the filling in problems?