i'm assuming the paperwork is in order
Well it may not be, if one includes the council administration of enforcement, and their website for submitting representations.
So you need to post all pages of the PCN so we can check it for fatal errors. Also check their pages for submitting representations and look to see if the list of statutory grounds for an appeal shown on your PCN are present on their web pages. Past up screen captures if you are at all suspicious.
Councils have to obey the law and regulations the same as you, so if they don't, even if the contravention is made out, they cannot enforce it. This principle has now one a lot of appeals at London Tribunals for London cases.