bb curve 9320 no incoming or outgoing calls allowed help

hi folks i have a bb curve 9320 which i brought of a facebook selling site they told me it was on giffgaff but had no sim card in it to see it working ,when i got home a tried a o2 sim card in it a new one ,acording to the phone its unlock,i get the signal bars coming up and it says o2 but when i try making calls or people try phoning me theres nothing,can anyone help me out please,a friend checked my ime number he said ,and told me it was`nt blocked ,i have no idea whats wrong so if anyone could help that would be brill thanks

Seems a bit strange, usually its because they are blocked/stolen. How did your friend check whether it was blocked or not ?Ange xx