When your android phone is not safe you will notice lots of symptoms. You need to restrict any unwanted activity. Be conscious of cybersecurity.
1. Unknown application 2. High usage of data 3. Phone battery drain fastly 4. Poor performance 5. Unwanted pop-ups.
1. Unknown calls and messages are being done. 2. No signal on phone.
You need to uninstall unwanted app by: Setting -->Apps Manager --> Uninstall The are the main cause of malicious attack.
To disable unknown source: Setting -> System Advance ->Developer option-> Navigate and disable
Choose any trusted antivirus software and scan your phone completely.
Open Google one app -> Tap storage -> Setup backup data -> Tap manage backup -> select backup now
Press the Volume up button and power button. Android recovery screen -> wipe catch partition -> yes, delete all user data