iPhone App Looping Issue

I have an iPhone 11. I have had nothing but issues with the app. Either I cant view my full account history- bills - any account changes - because they either give me an error or the page is blank!!

I cant even get T-Mobile to send out  invoices from June - July 2023. The app gives an error message for this billing cycle. 
I find it strange since this is the billing cycle where I my plan was changed wohltut my consent- and I’m  the only authorized user on the account.

I was told that was because  of the “old data system” that gives authority to all members on the account to male authorized  changes???? 

if this was the case, why didn’t T-Mobile notify all account owners that anyone under the account can now make changes without prior authorization from the. primary account holder - account owner?

IMO this is just unacceptable and unprofessional .