T-Mobile’s purported privacy center is a scam - neither the “do not sell” nor the “personal data request” “personal data deletion” functionalities work
This is probably by accident, not design. In general their web sites are partially non-functional. I am a T-Mobile customer and about 50% of the time I can't even log in and get a non-specific "our wires are crossed" error. Usually clearing cookies or resetting my password fixes it.
I don’t doubt that it’s incompetence over nefarious intent, but at the end of the day, it’s fraudulent/scammy/deceptive to say “you can opt out anytime” when that’s clearly not the case. Furthermore if the website didn’t work, but you needed to opt-in sure that’s their loss, but due to the misalignment of interest here, what may be incompetence has dark/nefarious undertones