According to several NC county policies I looked at, and if yours is similar, excessive absences regardless of whether they are excused or not can result in a failure. Did you make up any assignments/tests that were missed? Further, an absence is not considered excused unless a note is submitted by the parent and sometimes a doctor. that is pretty much a requirement across the board with the language being that a note shall be submitted for it to be excused.
You should be able to find your county's policy in the student/parent handbook every school normally hands out at the beginning of the year. About the worst you might do is report them to the state if they are not abiding by NC's compulsory attendance laws but that ain't gonna change the "F"'s on your report card.

