Turn on Airplane mode
Disconnect from Wi-Fi and mobile data
Restart the phone in Safe Mode
Uninstall suspicious or unknown apps
Remove apps with device admin access if needed
Clear browser data and downloads
Run Google Play Protect scan
Install a trusted mobile antivirus app and scan
Update Android and all apps
Change passwords for important accounts from a clean device
Enable two-factor authentication
Back up important files
Factory reset the phone if the problem remains
Restore only essential data after reset
Avoid installing apps from unknown sources