Why is my BlackBerry 9900 failing to register?

Hello pipo. I purchased this
new bb device 9900 from
China. I am from Zambia and my carrier is MTN Zambia. I am having. A problem in having the device register on my carrier's network. They say that they can not activate BIS because the device can not be recognized on their network and yet the device is not even branded. I get no response even when I try to register the host routing table.
The device is also asking for Enterprise activation.
My overseas seller seems to be
unresponsive i'am able to make and receive phone calls,send and receive text messages.....please help

I believe your phone may have an IT policy.

Update or reload your OS using BlackBerry Desktop software.

For more info search :
" remove IT policy from BlackBerry "