All boilerplate stuff. Where did this alleged contravention take place? The name of the car park?
Can you get a clear phot of the signs with the terms at the location? They are claiming that the signs included mention of the £70 fee. We know it is a lie that it cost them £70 to engage a debt collector when they in fact operate on a no-win, no-fee basis. The governments own analysis of their costs in the Impact Statement issued earlier this year show that on average, it costs the PPCs less than £9 per claim (not per PCN) in recovery costs.
Anyway, a phot of the signs would help if possible.
With regards to their mendacious statement about VAT, you should report them to HMRC for suspected VAT fraud. There is no comeback and it takes literally minutes to do so online here:
Report tax fraud by a person or business to HMRC - tax evasion, VAT fraud, false, Child Benefit or tax credit fraud.
Whilst the PCN is non-VATable, any debt recovery fee is definitely liable to VAT and they have not answered the second question asked in your response to their LoC.
You can tell that you are dealing with intellectually malnourished individuals by this little bit in their response:
Had you of paid...
You are now waiting for the N1SDT claim form to arrive from the CNBC. When it does, show us the Particulars of Claim (PoC) and the issue date and we will provide guidance on the next step which will be the Acknowledgement of Service (AoS) and any deadlines.