Bis problems on unlocked at&t blackberry 9900

Hello everyone, I bought an at&t blackberry 9900 from the USA, I reside in zambia. I had the phone unlocked by requesting a code from at&t. The problem I have is when I subscribe for bis in my country, I get a message confirming subscription But I still can seem to browse, even if I buy data bundles I still can't browse. I have tried reregistering the phone on the network, I have tried adifferent mobile network but still no result. When I subscribe I can see the blackberry logo net to the network bars. Also I have tried using different APN's but still nothing. Is there anyone that can help with this. Or any Idea what the problem is?
One last thing, I have previously had the exact same phone but the one I had was only 3G, on the other hand this new one is 4G. Don't know if the 4G model can connect to bis.

Have you looked at this?
MTN Zambia, MTN Mobile Telephone Networks. - BlackBerry�

Hi I went to my mobile provider and they said phone might still be locked to the at&t servers so I got in touch with an agent there and back they requested my pin, after I gave it to them they said my pin was not locked or active on there servers. I tried browsing using wifi and it was successful. When I run network diagnostics it gives the following.

Blackberry registeration :yes
Connected to blackberry :no
BlackBerry pin-pin : abort

It's like the phone cannot connect to the bis servers

I went back to my mobile provider and they said maybe the phone is locked on the blackberry servers

Does this help? How to Activate BlackBerry Internet Service | Chron.com

Service books maybe?

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