I can't receive BBM messages from certain contacts! Help!

Hi! I've been using BBM on my ancient Curve 8520 since January 2012, and it has not given me any problems. Until yesterday, that is.
I live in Pakistan. All my contacts from UAE are complaining that they can't message me. They can receive my messages and pings, but I cannot see their replies. In fact, my messages are left marked as 'delivered', not 'read' - even though they have read and replied to me. I can only see a few UAE contacts' recent updates. I tried deleting and re-adding one of those contacts, and I don't think they have received my request. My mum however (who is in Pakistan too), can receive and send messages normally with her contacts that are in UAE. I can send and receive messages normally with all my other friends and relatives in other countries. It's only a problem with my UAE contacts. This makes it seem as if there is something wrong with my phone. I have tried battery pulling many times, and have turned off - turned on all connections, too. How do I fix this? Help meeeee :crying: