I've been fighting this issue for some time now..
I've opened cases with MFL and like most things got zero help aside blaming it on my carrier.. I spoke to my carrier numerous times with them confirming each time there are no blocks on their end..
and after talking with many others (with different carriers) who have the same issue the frustration is real!
the crazy thing is I'm in a number of MFL Dynasty Leagues.. over time the mobile text option worked like a champ.. in all of them.. now it currently seems to be working in 8 of my 17 MFL Leagues.. I've gone through the settings backwards and forwards multiple times I am still unable to find an answer..