Are you a 1099-sub contractor of an install firm or a direct employee of the install firm?
Are you sure Time Warner is charging for materials? or is it the install firm charging you? If the install firm is charging you as a 1099/sub, then ask to see the latest BOM (Bill of Materials) from TWC.
If you are an employee of the install firm and they are charging YOU for materials to do installs .... RUN AWAY. Get a new job NOW.
If you are an employee of the install firm for quite some time, and they have been charging you for materials ...when you quit, call a labor attorney. You have back pay coming.
Good Luck