Customer Service Guy Made a Mistake. Nobody Knows How to Fix It

Long story short, I had an account with T-Mobile. I asked them to put a military suspension on my line. Military suspensions are 39 months long. About a year after the suspension started, I needed to access my phone again to gain access to an old account, I contacted support, they lifted the suspension, and then I asked the customer service rep to reinstate the military suspension. He messed up and instead emplaced a TEMPORARY suspension for 90 days.
After the 90 days, my account started getting charged for service again without me knowing it. After not receiving payments and incurring late fees, T-Mobile moved my account to collections.
I was never contacted by any collections agency. They never e-mailed me or called me. The only way I found out was (after my friend informed me someone else was using my number that was supposed to be on suspension) I called T-Mobile.

In other words, if I hadn’t called T-Mobile, I never would have known my account was sent to collections which means my credit took a hit because someone messed up on my account.
I called T-Mobile customer service, they told me I need to contact the collections agency, VoiceStream Inhouse VST, at 800-937-8942 but this phone number connects me to the generic T-Mobile customer service. And even then, nobody in the billing department knows what to do. None of the supervisors know what to do. One of them actually had the nerve to tell me to hang up, call the number again, and hope that someone from the collections agency picks up the phone! My credit is affected by someone’s mistake. I paid my bills on time when I was a customer, and now none of the customer service reps know what to do.