Well, we went through the toll bridge in late Nov, and back the same day (within hours) and 1 week later got a charge in the post for 3euro, so I went online and paid that charge and the charge for the return journey which was there too, so I paid 6euro.
A few weeks later I went through again, this time I was going to the airport and would not be returning for 1 week. When I returned, there was a letter stating that I owed them 3euro and a penalty charge for 3euro.
So I went online again, only this time there was only the charge for my going up to the airport, not my return journey. I challenged the charge, paid the 6euro that I rightly owed, and a few days later, got a letter to say everything was ok.
They are not consistant, but I think a lot of it is computer generated.