Hi, not sure if u got it fixed yet but here is my input, hope it helps
For the text message notification not working on Galaxy S6 or similar. I got a solution from cust. support. Follow these steps in order: go to Apps, Settings, Applications, Application Manager, Messages, click Force Stop, say yes, then click Storage, clear data, go back one step and see Notifications. This should not say blocked. Mine said blocked even though everywhere else they were "on". This fixed the problem. Let me know if it works!
Sent from my Verizon, Samsung Galaxy smartphone