Blackberry curve call failed?

i got a second hand blackberry curve 8520 when i got it worked for 2 days then it i got a call failed error message when i try and call if i call 999 it says "phone not allowed mm#5" the phone is unlocked to any network it was originally on o2 and i am using an o2 sim card i called o2 customer services and they said there is no barr on the phone. and my internet,BBM,msn still work where ever i go and i get a descent signal. i ran a diagnostics test everything was fine i pulled out the battery multiple time and got a new sim card from o2 still didn't work and when i check my status it says there's no service. i know this problem is popular but i couldn't find an answer to solve my problem so plz help me and also i tried other network sim cards in the phone to like t-mobile orange Vodafone also i updated it to the latest os