Consumer Cellular Mistakenly billed for line they incorrectly assigned, now refusing to refund my money Portland Oregon

I have used Consumer Cellular for years and been very happy with their service.  So I am still shocked over the issue I have with them now.

In December of 2011 I decided to get my elderly parents a cell phone for emergencies.  I called Consumer Cellular to order the phone for them and have it billed on my account.   I was very specific that they needed a phone with a number and area code in their state - Michigan.  I am in North Carolina.  I was very clear about that. 

Consumer Cellular sent them a phone and they got it an activated and when I checked online about it, I found they had assigned a North Carolina area code.  I called Consumer Cellular immediately to report their mistake.  They admitted it and said they would assign a new number with the correct area code and send a new sim.  They said to throw the old sim away and put in the new sim, then call to activate the number.   They said they would cancel the old number since it was no good.   We followed all the instructions and I did call Consumer Cellular back to make sure everything was correct.  They assured me all was fine.

I used their online site to not only get the amount owed for my bills, but also update my plan when needed.   The online site showed 2 lines, 2 phones, one for me and one for my parents.  I paid the amount due on time, and usually ahead of time.

On 11/13/2013 I was looking over the paper bill and noticed a 1 line charge at the end, for $20.00.  It was for that incorrect number that they had assigned back in 2011.  I immediately called to report it.  The woman in customer support looked it up and agreed, it was a mistke on their part, she said, "we should have cancelled that number and no one ever carried through.."  She added that I was owed a large refund and she was sending the billing department a note and someone would call me with 24 hours.

No one called me, so I called back on 11/14/2013 to find out what was going on.   I was told at that time that it was up to the discretion of the billing department to give refunds and they had decided not to refund my money.   They said they would refund 1 month of the overcharge.  I was shocked and asked to speak to a supervisor.

The supervisor said the same thing, that they had made the mistake, that they had not cancelled the line properly, but because I had not caught it they were not to blame.  He said they would not refund the money.   No matter what I said - pointing out that they had made all the mistakes for this overcharge - he said there was nothing more they would do. 

The amount I paid is around $500, or possibly a little more with taxes and fees.  They acknowledge the mistake.  I have only 2 phones and the original line they assigned incorrectly was never used.  It's in their notes on the account.  But they refuse to refund the money.

I am incredulous over this.  They basically said, if you take something from someone and they don't catch you, you can keep it.  I wonder if they would feel the same way if they had an employee take 20 or 30 dollars a month from an account and they didn't discover it for a few years.  Could the employee keep the money?  After all, they didn't get caught.  

They originated the mistake, they said they had cancelled the line, they were at fault right from the beginning.  They continued to bill me for a number that was never used.  There was not 1 minute of time on that line in 2 years.  And they can't refund my money because I didn't catch THEIR mistake??? 

I only thought ethics in business was gone, now I know it is.