mobile

I got s4 i337 phone issue is that this phone I unlocked with z3x was working properly now phone shows no network doesn't pick network signal when I dial *#06# phone shows original imei i did repaire imei when type *#0011# in service it shows imei cert NA I also did write qcn file but no luck after i flashed it with latest version 4.4.4 nothing work and still the same problem persists. Help me with this issue plz