The police summoned me by private phone to assist in the investigation. Will the police issue an officer's card to prove themselves?

No, according to China Travel Service. Com, the public security bureau will use the phone of the unit or come to the door. The public security bureau will not inform you by sending text messages or making personal calls. If you receive some phone calls or text messages with mobile phone numbers or ordinary phone numbers, they are all fake. For illegal acts found on the spot, the police station can summon them orally. For illegal acts found off-site, the police station should use a summons card, and generally do not use telephone notification.