T-Mobile Phishing

I got a couple calls today from people claiming to be from T-Mobile using a restricted phone number. They said that I'm delinquent on a $156 bill from 2004 and that they were going to report it to a credit collections company.

I called T-Mobile directly to verify their claim and was told that I left everything in good standing (I've been with Verizon for the last couple years). After I called T-Mobile, the "collections" people called back. Fortunately, I didn't give them any personal information on the earlier calls. Once I told them that I cleared everything with T-Mobile and that I wouldn't give them any information, they immediately hung up.