Overcharged for honest mistake

I dropped off a family member at OR Tambo International Airport on the 18th January. I am not a frequent visitor at the airport and found the parking signs confusing and mistakenly parked in the Long Term Parking, I was parked there for just over an hour and upon my return was subsequently charged R540 which is in line with the long term parking tariff. I paid the ticket, however whilst walking to the car I was advised by a friendly guard that I can approach the Parking Office to obtain a refund. I went to the office and was advised by the lady that had I not paid, she would have been able to change the ticket so I paid the short term parking tariff. Because I paid she cannot refund me, however she advised I email Dineshri Aboo to query the refund. I email Dineshri on Saturday who forwarded my request for a refund to Mantsadi Moloi, whose response was my refund request is declined as there are numerous signs which indicate the parking bay where I parked is long parking and long terming parking tariffs apply. I feel this is unfair, I am not a frequent visitor at the airport and it was an honest mistake parking in the long term parking. I do not feel it is fair to be charged R540 for parking at the airport for 1 hour and 10 minutes, my ticket which I provided clearly indicates this. The lady at the office on the 18th confirmed she could have amended the ticket had I not paid, so why is it I cannot be refunded. I feel this is really poor customer service from ACSA.