Who I have the same questioned this topic

Galaxy s5 won't receive call from wife's office number(landline) to her cell. When her employee's try to call her they receive a busy signal. If they dial the area code for cell it goes right thru. I also have s5 and tested this with same result. Just started yesterday. As best I can tell this is the only number that does this. Both phones seem to be working fine otherwise. ???