Escalate customer complaint

Hi, I’ve been an AT&T customer for close to 20 years. Up until August I was on a grandfathered cell plan that included HBO. I am also on a grandfathered Direct TV streaming plan, as I signed up on the first day those services were offered. In August I chatted with an AT&T rep about hotspots. I did not have hotspot service on my plan. The rep suggested I move to another plan for a $1 cheaper per month but it included hotspot service. At the time, I knew that meant going off my grandfathered plan, so I explicitly asked if I kept HBO. I was told yes (and have screenshots of the chat). About a week ago I got an email saying I would be losing HBO because I changed my cell plan earlier this year.  I tried calling AT&T and was told at first I could be put back on my old plan. Then she said she couldn’t because it had been greater than 90 days. I feel like that is not my fault as I had no idea there was an issue within the 90 day period. She told me that she would send feedback to the supervisor of the rep I chatted with in August as I was given wrong information about keeping HBO with my new plan. But I’ve heard nothing from AT&T about my situation.  I feel things were wrongly conveyed to me and now I have to risk paying more money to keep HBO.  Can anyone help me figure out how to escalate my request for assistance? Thank you.