I bought a new blackberry a week ago but bbm isnt working?

About a week ago i bought a new blackberry to begin with it wouldn't work with recieving calls so i called them up and asked .. it was something to do with a setting on do not disturbe! So everything is fine now apart from the bbm cause i can add people and they add me but i never get their invites and they dont get mine. I spoke to my friend about it but she has the blackberry bold and i have the curve 8520 so it is confusing as we have completely different settings .... HELP!