Tfl parking notice postal delay

JimSmit

Received parking notices from Tfl. The first incorrectly stated that I hadn't challenged the parking notice, and was due in court. I called and they confirmed they had an issue sending out the letters, recanted and accepted the challenge.

The second notice, they claim the challenge was received too late. It was challenged online the day the letter was received in the post. They claim I am responsible to pay for receiving the notice late.

Any tips on how to prove that it wasn't an error in my side?

Thanks.