Free Traffic Legal Advice

So you received the original PCN sent by post, paid the toll but not the penalty charge. You then ignored the matter until this OfR arrived. There would have been a second statutory document called a Charge Certificate sent out before the OfR. Did you not receive this ?

Anyway, sorry to tell you that by totally ignoring the PCN, you have forfeited all possibility of getting the matter reverted back to the PCN. Normally when an OfR arrives we advise people to submit a TE9, but your circumstances are not such as to allow you to submit one.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1094509/TE9.pdf

So your only option is to pay the sum demanded. If you ignore this OfR, the council will instruct bailiffs to obtain the money, and they will also charge their own fees. It is important to remember that the bailiffs will be seeking payment, and can seize goods of any description to sell and pay the debt.

Thank you - I didn't receive the Charge Certificate. The only thing before this was the original PCN.

I'm pretty sure the PCN warns you in stark terms not to ignore the notice, and that ignoring the notice results in you losing the right to appeal, and all sorts of additional costs being added.

You've ignore the PCN and now you have lost the right of appeal and all sorts of costs have been added.

In the circumstances, the only thing you can do is pay before the charges go up even more. Ignoring a PCN is the one thing that you should never, ever do.