1. root your phone ( for 6.x.x you have to downgrade to 5.x.x and choose this rom: http://download.ztedevice.com/device/global/support/product/541/5878/sd/2016041911215705.zip)
  2. unlock using Qcom smart latest in 'ADB MODE'
  3. after reboot don't press ok and re-root phone again.
  4. select 'OK' and wait until rooting operation finishes and reboot the phone manually
  5. unlock done

P.S: if the procedure fails in step 3 and security phone is damaged don't panic ! just repeat the unlock procedure and select backup when program prompt.Then start unlock from the begining.