I am being harrased by text msg and must know ASAP :how do I block text msg in the Moto G 4 plus?
in Google Messenger has a block sender option (really just archives it but you never see it)
open up the message thread from the contact you want to block
tap the 3 vertical dot menu in the upper right
tap People & options
there will be a block option (with the number being block listed)
If you are receiving messages from some commercial site, collection agency, etc. they might be coming to your underlying T-Mobile or Sprint number, not the main number on your phone. Are these messages coming from a party you are familiar with? If not, they are likely coming to an underlying number previously held by someone else.
If that is the case you can open a service ticket and ask RW to change your underlying number.