Escalation of Customer complaint process

Hello,

Is there a better way to escalate customer complaints at T-Mobile? I was only given a fax number and a mailing address for the Executive Response team, with no email address or phone number. It feels outdated—who faxes these days?

Regardless, I was able to find a way to fax them, no one has returned my message or even acknowledged receipt of my complaint.

I am looking for an alternative method to escalate my complaint, short of going on social media to publicize the poor customer service. If I were the business owner, I would want to know and address the issue before it becomes public.

Any guidance would be greatly appreciated.