T-Mobile My phone line moved to Sprint without my consent Nationwide

I have been a T-Mobile customer for over 11 years. This past December, 2015, one of my lines have been transfered, without my consent, to Sprint, by a person I am not affiliated with in any way.

I called Sprint and T-Mobile hundreds of times but nothing has been resolved.

I've had the phone number linked to various bank accounts or online accounts, therefore someone using it may gain access to my personal information, which is a scary thought.

I requested from T-Mobile to at least block that number to be used but they couldn't do anything since it belonged to Sprint. However, 3 days later, a different name transfers the same number (my former number) back to T-Mobile!!! Called again T-Mobile / Sprint asking to investigate what's going on - a line has been moved from/to T-Mobile by different names. The investigation is nowhere; I filed a police report, a FCC complain, etc.

Interestingly enough, Sprint actually assigned a person to look into the issue and they even called me twice. T-Mobile has NEVER bothered to get back to me.

I am tired to fight them. In the meantime I open a new account trying to protect myself.

Any advise would be appreciated. T-Mobile ignorance and lack of involvment have been very frustrating. I am still waiting for the investigation to finish (if ever) and switch to a different provider but I would hapily sue T-Mobile for the lack of security procedures/protocols.