Only a couple of weeks ago I got a letter demanding £70 for over staying my visit at Aldi then the penny dropped... I had forgotten to key the number plate. The letter showed my time of arrival and the time I left.... a total of 35 minutes. Fortunately I still had the receipt as it only happened 3 weeks before or so.
I took a picture of the letter and receipt and emailed Aldi at
customer.service@aldi.co.uk 2 days later I got a reply saying they would ask the parking administration company to cancel the fine and they cancelled it.
Failing that I was prepared to sit tight and not pay it. I did write to the company and explained why I should not pay £70. I said that I forgot to enter my number plate and I did not overstayed. ... never got a reply from them. The legality of these fines is very questionable and lots of people are fighting them.
I was going to send a cheque for £1 as I considered that is the current rate for 1 hour parking in the area.
Edit:
After I got confirmation from the parking company that I was off the hook

I wrote to Aldi to thank them and also to say I would never shop at Aldi again. That I was lucky to still have a receipt otherwise I would have had to pay the fine for 35 minutes of parking.