1. Signal problem: If the signal in your area is poor or there is no signal coverage, the mobile phone will not be able to dial and receive normally. Try to restart the phone or change the operator in an open area to test whether the call can be normal.

2. Wrong number: If the phone number entered is wrong or added to the block list, the phone cannot be connected. Please check that the dialed phone number is correct and make sure it is not blocked.

3. Mobile phone failure: If your mobile phone has hardware failure, such as signal antenna failure, SIM card failure, etc. , which will lead to the inability to make and receive calls normally. It is recommended to check whether your mobile phone has these problems, and try to replace the SIM card or repair it.

4. Operator problem: Sometimes it may be because the network or operator in a certain area has failed or stopped, resulting in abnormal telephone communication. You can find out the local network situation and whether there is downtime or failure by consulting the operator official website or customer service.