"Problems with Parking Eye"

I have been issued with three parking eye tickets. For the first, I could not walk down to the paying meter and back up again and then back down again. It's unfair that there is no system to pay at the level where you have parked. The other two were at the 20-minute slots. For these, I tried to buy tickets, but the machine said that I had to insert £3. 00, whereas the ticket should have been for £1.50. One of them claimed that I had stayed for more than 20 minutes, which I hadn't. They took one photo whilst the car was parked, and the other when I was driving out of the car park. What is worse, they send the tickets by post and I have been staying with my daughter for the past three months. I don't really need to check my post because I pay for everything automatically. I only went by the flat briefly recently to see whether I had left anyone off the Christmas cards list - just to check on Christmas cards. I think it is outrageous that a machine can fine you for something without informing you at the time of the fine. Is this in fact legal? How can it be?