Im having the same problem to which i found out after switching phones but still using the same service. I still have my other phone and it works great, the new one wont send notifications. Its a Generic Brand from metro T moble and the other one is a LG Stylo 4.
I wrote up a comment about it in the General section of this Community. It has something to do with the Quality of the phone itself, cheaper brands dont want to work properly especially getting notifications.