Suggestions

1. Root the device and you have full control.
2. Disable updates on mobile data and don't use Wifi.

Suggestions

1. Root the device and you have full control.
2. Play Store > Your Icon > Settings > General > Network Preferences > Auto Update Apps > Don't auto-update apps. This might still update system apps.
3. Play Store > Your Icon > Settings > General > Network Preferences > Auto Update Apps > Over Wi-Fi Only and don't use Wifi. This should stop all updates.