Hotspot not working, att has given up

I can't get my wifi Hotspot to work at all. It used to work fine. I have spoken to dozens of agents and gone into the store. They tried all possible troubleshooting to no avail. They told me it was my phone and to buy a new phone. I bought a new phone. The Hotspot worked for the guy at the store. Brought it home and I can't get any device to work with it. I have full bars. The last agent I spoke to said he wouldn't blame me if I left att. Can someone please help me? I the solution to leave att????