Exclamation [Q] IMEI CERTI FAIL with N900W8, please HELP!!

Currently have a 4.4.2 n900w8 from bell canada, Imei and serial number all seem normal, but showing not register on the network when making phone calls.
What happened was I tried to get it unlocked in China but failed, after I got back to Canada it doesn't work anymore.
Tried to flash the stock rom and nothing changed, still same error.
When *#0011# showing network blocked and imei certi fail, checked with bell my imei isn't blacklisted.
Please, anyone can help me?? Just got this phone and really don't want to get a new one.