Lack of services - Device department

I bought a device from FNB (FNB Phone) a few months ago from a promotion they were running. The deal was that I could get the phone for cheaper but then my savings account will be locked during the time I'm paying the phone. After paying off the phone I was suppose to get an unlock code for the phone to allow me to use other sim cards in it (since I am forced to use an FNB sim only at the moment). I never received that code and have asked for it twice only to be told that they forwarded it on to management. Please advise and assist!