Unable to access att.com via safari

Upgraded from iPhone 8Plus to iPhone 13 six days ago and suddenly I cannot access att.com or currently/yahoo email login. Tried ALL of the recommendations: cleared all data/websites, deleted bookmark shortcut then re-saved, restarted phone. I have no problem accessing my account via desktop pc. Quite frustrated with AT&T as I have spent the last 4 weeks resolving an open FCC complaint and now this…..