Unable to use our provided HBO MAX Benefit

We currently have the Unlimited and More Premium Plan that includes HBO MAX.  We have not used HBO MAX through ATT because our internet and TV were through XFINITY and it included HBO MAX.   We have canceled our cable and I am trying to sign into our HBO MAX through ATT and it says that I don't have a subscription through this provider.  I checked my account details with ATT and it says that we have HBO MAX included.  I called customer service and they told me that it isn't included in my plan.  But my plan says it is, and the list provided on this website of grandfathered plans also show it included.  I find this ridiculous that this is such an issue.  I asked the agent and the supervisor I eventually spoke to "why does it say it is included, if it isn't?" They have no answer to that except that maybe the system hasn't updated.  And after all of that they had the audacity to try to sell me more phones when I'm just trying to get the services I'm supposed to have included. Obviously loyalty doesn't matter to ATT.  We have had service with them forever but obviously they don't care about that.