As I understand your narrative, you have totally ignored the PCN, and also the Notice to Owner which would have been sent to the name and address on the V5 Registration Certificate for the vehicle, plus you have ignored the Charge Certificate as well, which puts the penalty at £195. True ?
YOU haven't mentioned the Notice to Owner, or the Charge Certificate documents. Did you receive these ?
If true you now have no option to submit any representations at all, only the payment option. This is because there are fixed periods on the PCN, and also on the Notice to Owner, to submit representations, but you haven't submitted anything. Any particular reason you have ignored all their documents ?
Their letter you have posted is not an enforcement document within the legal enforcement process, (Parliamentary Act, plus regulations). It is an unofficial document inviting you to pay the £195 before they register the debt at the Traffic Enforcement Centre. This adds £9 to the amount, making it £204. They will then issue an Order for Recovery which can be paid, but there is then a back-stop process to cover cases like PCN/Owner not received. However this doesn't seem to fit your circumstances.
Really, if you can tell us why you have done nothing to either pay or submit representations it would help us to see if there is anything that could get the process reverted.