My passport and visa already expired for long time. What can I do?

Hello to all. I'm a Cameroonian living in China for 13 years already. I have where I can pay my overstayed to police. But the Chinese police told me to go to my embassy to extend my passport before they can give me 10 day leaving type. I've been trying to call the Cameroon embassy in Beijing but no one pick the call. I need some help please