Agreed, just ignore it.
I once got a parking fine when I parked the car in the private car park belonging to the block of flats I actually lived in at the time. They claimed I was in a no parking zone and started sending me letters demanding money. I replied, with photographic evidence, to show I was several metres from any signs that even vaguely resembled no parking signs, therefore had done no wrong. They replied stating their case again, so again I replied stating that there is nothing to indicate I shouldn't have parked there. They replied and said that there was a dark coloured brick pattern in the road which represented a turning circle, which I had blocked, apparently dark red bricks mean no parking it's a turning circle?

Replied again and told them to check the highway code, as it was absolute nonsense.
A while passed and I received a letter with
HUGE RED WARNING WRITING stating they may take legal action if I did not pay. Naturally I sent another letter back, also in huge red writing, saying that I had no intention of paying.
I moved not long after and never heard off them again anyway
