HBO Max not working

I get HBO Max for free with my AT&T plan but for the past month it hasn’t let me watch anything. I’m signed in on HBO Max, but when I try to play a title, it will tell me to resubscribe. I’m not streaming on any device other than my TV. I’ve tried logging out & signing back in. & I have went through all the troubleshooting tips on HBO Max’s website. Nothing has worked.