My mobile data connection is not working even though it shows 4G signal and am not able to either send or receive messages
try resetting your mobile settings
settings -> system -> reset options -> reset wifi, mobile & BT
if this doesn't help then please try using someones elses SIM card so see if you can send messages with that one. Sometimes just by exchanging the SIM, things start to work again. Just like a restart can solve all kinds of weird issues.
I'm having the same problem!