I'm sorry to hear that you're struggling with this issue with your teen. There are a few different approaches you might take to resolve this issue.
First, you could try blocking your caller ID when you call your daughter, so that she doesn't know it is you calling. Your phone company can give you the code or service information to access that feature. However, this doesn't guarantee that your daughter will answer the phone, and you obviously can't overuse this feature (or else she might never answer the phone when it says "private" or "unlisted" number for incoming calls).
Depending on the phone your child has, you may be able to leverage GPS cell phone tracking software to see the real-time location for your child's cell phone. Here's one example (and the phones they support):
http://www.accutracking.com/
This information could be helpful for safety reasons, as well as to determine if your teen has the cell phone with her at the location she has provided for her whereabouts.
You might also establish a rule with her that if she doesn't answer your calls, or return them within a certain timeframe, then she will lose access to her cell phone for a set period of time (a day? a week? Set a reasonable time based on the severity of the behavior, and/or the number of times she's ignored your calls). You would obviously need to be flexible if there was no service in the area she and the phone were located (such as in the woods or at the beach, or anywhere her mobile service provider's network doesn't reach). Contact the mobile service provider for their network coverage and/or any related outages on the day you are trying to reach your daughter.
I'm also including below some additional resources you may find helpful to your situation. Good luck!