Ah Sweetie I'm so sorry that your parents are making you quit. First thing you need to do is talk to your Pledge Mom and treasurer. Most chapters have payment plans. So maybe between your parents, and your own savings/job you'll be able to stay.

If that isn't a viable option; you should be able to depledge as long as there isn't any money already owed to the chapter. (Like pledge dues, etc.) All this is assuming you have not been initiated.
If you do have to depledge maybe you can save your money and pledge next semester.