need police clearance from Changchun.

Momin, I am afraid that Chinese embassy can't help you acquire police clearance. You need to ask help from the notary office in Changchun. They are capable of helping you acquire the police certificate. In this way, you need to go back to apply. The process is that you find the notary office. Then they usually send an investigation letter to local police station. After they get the police clearance, they will notarize it for you. Then you can use it.