I used Dublin Airport Aer Rianta Car Parks recently and had some difficulty with the ticket machine before picking up my car. I kept the receipt for 38 Euro (4 x 9.50 per day) but noticed my Visa was charged twice at 36 Euro each or 72 Euro in total, which is very strange. I'm now trying to resolve with Aer Rianta DAA. Luckily, they matched my Reg # and my receipt number.