For balancing redox reactions we use mean values for each type of atoms.
In organic chemistry, sometimes, we calculate ON for each carbon atom. We just break all C-C bonds (single, double, triple) and calculate oxidation number for each carbon and other atoms in direct proximity, ie for CH2=CHCl as if CH2 and CHCl were isolated (ON for C -2 and 0 -- mean value -1).
Your reaction is wrong. Chlorine undergoes addition to double bond forming CH2Cl-CH2Cl. Of course, you can obtain vinyl chloride from ethylene chloride by elimination of HCl, but this is quite different type of reaction, and you should write down two independent reactions.