Samsung GS4 (SGH-M919) - Did factory reset on encrypted device...can't get in with correct key

My office just switched mobile providers. We retired a number of Android phones. Due to our devices having Protected Health Info we encrypted them.

I couldn't find the menu item to do a factory reset (thank you, fix million different layouts of Android menus.) I performed a factory reset using the Volume-Down + Power button function. The phone appeared to wipe the user data and cache partitions and rebooted. I didn't decrypt the phone first and I think that may be why I'm now prompted for the encryption key to use the encrypted device memory. The same storage that I wanted it to wipe out and return to factory state. (I read that the factory reset option doesn't really wipe things out as one would expect.)

When I enter the key I briefly see the green outline of the Android logo then the screen goes black. I know it's accepting the key because if I intentionally give it the wrong key it will repeatedly say, "Try Again." When I plug the phone into my Mac it is recognized as a network interface.

I'd just like to get this phone to a usable state again. I have no desire to keep any of the data that was on it to begin with. Tips or suggestions are appreciated.