Security, Social or routing?

I got a call "from Social Security".

Or was it?

The call was from a local Maryland {301} prefix. (That number belongs to
Envoy, a telecom carrier I'm aware of.) But she wants my data (SSN, etc.)
before she'll talk & I want proof of her status before... Mexican Standoff.

She suggested I call my local office to verify she is an employee.  She gave
me her "800" number, and a ten-digit (!) extension. {The extension's first 3
digits were …

amp aware call carrier data envoy etc local maryland proof routing security social social security ssn telecom