Returning to the original subject, if you forget to pay the charge you usually get let off the fine (at least I did).
Mine was a little more complicated - I have an account with them but forgot to tell them I'd changed the car. Alas DVLA had got my address wrong - I didn't know this, I just noticed I hadn't received the log book and applied for a duplicate - so all the paperwork went to a different address, including a county court judgement. A year later I got a very persistent debt-collection agency demanding hundreds of pounds in fees and making daily threats. Took a while to sort out, but eventually they rescinded the court order, cancelled the PCN and charged me £2.50 as a "first time offence". Presumably they had to pay the court and agency fees. Ex AA Series III LWB Safari - Gone
300TDi Disco (bought new - terrible car) sent back after 18 months
Freelander 1 Estate - leased, given back at end of lease
200TDi Disco (bought from a mate with 100,000 on the clock) - Gone
Disco 2 TD5 - sold and exported to France
FR2 TD4 GS - Gone
FR2 SD4 HSE - Now changed for a DS
New model ex-demo Evoque S 180 in white
Unable to order a new DS, so gave up. Now have a Volvo S90 Recharge.