Sophos Mobile Security: how to remove Android SystemApp or disable scanning ?

Hi,

My question - how to remove Android SystemApp or disabling SystemApp scanning from Sophos Mobile Security? SMS has detected Threat (Andr/Gedma-A, app name com.mediatek.smsreg) on  Lenovo A7600-H (Android 4.4.2) Tablet.

These steps was done:

1. I have done factotry reset to that Device
2. I have disabled that App on device
3. I have created Sophos Mobile Security policy to skip System app scanning

Threat still detects and user can't use that Tablet.

Thanks for any suggestion.