Call detail records older than 12 months; CS says I can't get them

How far back does T-Mobile keep records? All I’m looking for are essentially the detailed bills as far back as possible to look for a specific phone number. Customer Service is telling me I have to have law enforcement/”authority”/”attorney” contact customer service, give them my information, then get transferred to a “back office” (I am quoting) to then make demand for my records; or, go to a T-Mobile store and hope there’s someone there that will understand what I am asking for, and then the employee can decide to send some form of communication to a “legal office” that the CS rep will not give me the direct contact information for, nor what the “legal office” is officially called. 

I’ve been a customer for almost 8 years, and I cannot fathom why I can’t get a digital copy of my past billing detail without having to “have my attorney” contact CS. 

CS doesn’t know how far back billing detail can be requested.

CS says there is no way to request these records through any department except via fax (which she says my attorney has to do) to a “Legal and Emergency Response” group. 

The reason I need these details is for a case I am investigating, I need to establish a timeline for one of my contacts as far back as I can.