I agree with most of the comments below, you had a bill that you didn't dispute that I'm sure listed the charges, and it's not up to AT&T to decide a line where it's customers might think a charge is high and inform them of it.

I will also point out that what is being charged to reach other counties isn't really relevent here. You yourself point out that Afghanistan is active war zone. I have to think that complicates communications some.