Hi Leesider,
I had a similar situation recently and when I rang to make a payment I was told the outward journey should have been paid the day before. I objected the 40 euro fine as I had only received the return journey bill and was waiting to pay for the two together. The staff member put in a dispute for the outward journey and said I would hear from customer service. A week later I received another letter requesting the 43 euro or go to legal charges. I rang once more and spoke to customer service this time ,they took the payment for 3 euro and wrote off the 40 euro late payment fine. They were very nice, well worth a phonecall, hope you get on as well.