Coverage Gulf of Mexico

So I’m working on a boat off the coast of Louisiana and phone working great. Then I get a notice of 200 MB usage used and phone stopped working. So I upgraded the International 15 GB of roaming for $50, and it says its on my phone, but phone still won’t work. Guys with AT&T are not throttled, but I am an originally a Sprint now T-Mobile customer. Any suggestions? Woty