Unauthorized insurance charges

I rented a car from Alamo at the T F Green Airport in Rhode Island. I made an electronic reservation for the car, a GPS device for the week, and on my E-reservation chose NOT to have insurance coverage since I am covered by my own insurance. When I arrived to pick up the car, I was asked three separate times if I wanted coverage, and three times I emphatically refused. Since I was in a line with several other people, the sales person whipped the document across the counted and said, "initial here, here, sign here," and so I did. He then printed out a recept, stuck it in the rental folder and directed me to the car lot. It was only later that I noted that the document included a charge of $160.00 for insurance. Every call to Alamo has met with the same response: you signed, therefore it's a legal document. However, this is clearly fraud which takes advantage of a rushed situation where people are travel-weary, hurried, and interested in completing the rental transaction. They are running a scam which relies of people's inattention to 'legal' documents.