Plan A... complain to Iceland about receiving an £85 speculative invoice from an unregulated private parking company for being a customer. Aim for the very top of the management food chain and email the CEO, Tarsem Dhaliwal, at Tarsem.Dhaliwal@iceland.co.uk and CC in yourself, showing evidence (receipt) that you were a customer on the day. Let him delegate it to one of his minions to handle for you.