Just to let you know, in case they prove to be obdurate, their PCNs are unlawful and have been since they came under notice at a 2018 adjudication at the Traffic Penalty Tribunal, (see file attached)
At the moment, it might be best to call them again, and tell them that you last used your Autopay account in 2022, so what has been changed to make it impossible for you to open your account.