Can't set up cellular on apple watch

Every person I talk to tells me they will solve my problem. Hours later and same error message. They say they will research it and call me back. Never happens. At the end of each hours-long call they ask me if there is anything else they can help me with. Ridiculous.

I have had the exact same experience. There seems to be no fix.

I had the same problem. Spent hours on the phone with ATT and nothing I found this and it works I have the new iPhone 12 pro and I used my husbands iPhone XS   ..hope the helps. 

Thanks, @AngelineP 

I saw that guy’s post too. I have the new iPhone 12 and my husband has an older one 6S. I did try to set it up with the SIM card switch with his and got the same error. He did not previously have an Apple Watch already set up though. Did your husband’s phone already have one set up? Thanks!

PT15

yes he had one but I unpaired his from his phone and unpaired mine from my phone

than turned both phone off and the watches. 
I took my SIM card and put it in his phone turn the phone and watch back on and connect them again. When it gets to the cellular say yes and set up you should get a message that is was set up. I don’t think it matters if he has a Apple Watch as long as you down load the app to his phone. It did ask me for the Apple Watch Apple ID and password. 

@AngelineP  Thanks. Maybe it makes a difference that he didn’t already have one that worked. I did download the app on his phone and went through the setup cellular process and still got the same errors at the same time. Very frustrating. Yesterday I talked to an AT&T person who said he wouldn’t give up on me and would call me back at 9 this morning. That didn’t happen.

PT15

did you have the Apple Watch working before?  When you go into cellular settings in the app does it show ATT?  

@AngelineP 

The watch works fine but cellular has never worked. AT&T shows but says not in use. And if I click it the only option it gives me is to delete it.

Pt15 when you set this up on the other phone ( after switching the SIM card ) you have to select add new plan. 

when you unpaired you did it by 

in app select all watches at top

select the I with the circle and than unpair watch 

when you set up watch again do as new watch

@AngelineP  I think I did it that way. I will try it again when my husband gets home from work with his phone. Thank you. You are way more helpful than AT&T. 😊