Mine is Lenovo a9 16. After I bought it, I locked the screen for a long time. There will be no signal, no phone calls or text messages. What's going on here?

Hello, the landlord can compare it with other mobile phones in different environments to see if it is only your mobile phone. If it is not a signal problem, it may be a problem with the mobile phone system. It is suggested to restore the factory settings of the mobile phone or upgrade to the latest version of the system to see if there is such a problem. If not, send it to after-sales service.