Do you have any male friends/relatives/neighbors that are car savy? If you do, and they are willing to help, this may be all you need.
Unfortunately, there are a lot of shops that try to take advantage of a lone female. Explain the entire situation to him so he is well informed, and will not be caught off guard. Have him read over any paper work and warrenty information you have from the shop, and then go together in person and ask to talk to the owner(s).
Look them up on
http://search.bbb.org/search.html, and see if they are a registered member. If they are, you have another tool.
If they are still being unreasonable after you meet with them, inform them that you are aware that they are a member of the Better Business Bureau, and that you will be lodging a complaint about their poor treatment and service. Then they may just change their tone.
Good luck. Let us know what happens.
Chuck