Z3x Team help Docomo SC-04 E

Hi support we have a problem with Samsung Docomo SC-04E which was specifically made for Japan. we have a lot of these here in Africa where most of the service providers uses GSM 900/1800. These fones turns to have a problem of network failure ,sometimes would work at times later no network and so fourth . anything the team could do to solve out this problem, I have version 4.4.2 which got unlocked ,Network full receives messege from the provider to configure mms and internet but cant call or receive calls. what do I need to do

Attached Images
File Type: jpg SC -04E.jpg (143.2 KB)