Free Traffic Legal Advice

Hi, I wonder if anyone has suggestions on how to resolve a parking issue.
I parked in the short term parking at Darlington rail station on the 4th January. There was a short train delay but I collected my passenger and before leaving I entered my car registration to check if there was any fee due.(20 min free parking) Nothing came up on the screen so I assumed I had nothing to pay and I left the station. On the 13th February I parked in the short term parking again and on exit I entered my number plate details again but I got a message saying number plate not recognised with a photo of a similar but different number plate. I tried again with the same error message. I saw a box asking to enter my number plate manually. This time a message came up saying I had overstayed parking by 40 days 8hrs and 18mins and I owed £437.50. I have not had any corresponds through the post and I am concerned the amount owed is still increasing. I have contacted parking@lner.co.uk twice by email without any response. I would like this issue to go away but I am unsure what to do next.