Hello,

 I am not a lawyer nor expert on this issue but I think you could still appeal. How can somebody change their status as soon as they were let go by the company. For most cases there is a 60 day grace period to change your status and as you said you were let go on Nov. & Applied for COS on Dec. which is still within the 60 days period. Please reverify that information, also do not hesitate to check with your school that you Graduated sometimes they may be able to guide you. Good luck!

Thanks