all my tv settings & cable box are set to English.why am I still getting nat.geo. in spanish?

Check the channel on https://watchtv.cox.com with SAP Off to see if it's Spanish.  If it is, then it's probably the affiliate as Bruce suggested.  However, if it's English, that doesn't necessarily mean the affiliate didn't broadcast a program with Spanish as the primary language.  The current program might just be English only.

View a program on an English speaking channel on your cable box that has an SAP indicator in the guide (Spanish when SAP is On)  to see if it's Spanish when your SAP is Off.  If that happens, your cable box SAP would be out of sync.  Cycle the cable box SAP On, then Off to reset it.  If that doesn't fix the issue, reboot the box.  Let us know what the issue was when you know.