Payments Made Towards My iPhone's Service and To Pay Off The Device's Purchase Price

I have been paying, via autopay, my monthly service charges and the actual cost of the iPhone, and this has been for the past 2 year.  I just recently found that my iPhone still had its original ~ $600 balance, no payments have been forwarded to it.  I thought that was part of my original Device and Service Plan Agreement.  The amount scheduled for its payoff was to be $30.41+ monthly while my service charges to be paid thru this agreement were ~ $45+ a month.

I am trying to figure out where the $30.41 monthly device payments went - Is there anyone here that can offer suggestions?

Oh, and also my iPhone has two IMEI numbers assigned to it.  The young man at the Xfinity Store said all iPhones have two IMEI numbers assigned to them.  Really?