Gladstones Letter demanding payment or legal action

[Guest]

I parked in a mostly empty brewers fayre car park one saturday for around three hours and came back to find a parking fine. Since then I recieved numerous letters addressed to me but with the surname incorrectly spelled. I stopped opening them and either binned or returned them marked as not at this address. Now, around a year after I parked I have recieved a letter from Gladstone Brookes asking for payment or legal action will ensue. Looking for what steps to take next. Help is much appreciated, thanks.