iMessage not working over cellular network
I have an iPhone 6 Plus and two weeks ago I updated to iOS 9.1. Since then, I have been unable to send/receive iMessages over cellphone connection (text messages are fine). I can send iMessages over wifi without any issue. It seems that also the notifications from apps are not being pushed over cellphone connection, since as soon as I connect to wifi I get many of them.
So far, I have logged in and out of the cloud, itunes, etc. I even reset the network settings without luck. Yesterday, I backed everything to the cloud and erased all context and setting (and got everything back from the cloud). It did not solve the problem either.
I would appreciate any help!
iPhone 6 Plus, iOS 9.1