U S A Payphones

I recently used a payphone in the Minneapolis Airport that advertised 4 minute calls for $1. I didn't have coins so I used my credit card. I read all the notices on the phone and it's surrounding space to see if charges were different for calls placed by credit card. There was nothing that talked about charges placed by credit or debit cards. Four days later (July 20th) 4 charges for over $16 were charged to my card. I was charged a total of $65.77 for 4 calls that were all very short. I didn't time my calls but I don't believe any of them were longer than 4 minutes. If they were, it was only by a minute or two, and that would have been one call out of the four. I called the company and they told me that I should have asked to talk to an operator before placing the calls. I said I didn't know that was an option, and even if I had known, it didn't occur to me to do so since the price for calls was clearly displayed on the phone. They offered to refund $20 out of the $65.77. I asked to speak to a supervisor but none was available. I asked permission to leave my name and number so that a supervisor could call me back. They said they don't make outgoing calls.