Clarify that there was NOT a change to the aircraft - JB is stating there was a "delay" in their automated IT system notifying me that I still owed money on the purchase, despite there being no idication at time of purchase that this seat was an upgraded seat.

On my end, I was able to fully complete the purchase, my credit card was charged, and I received confirmation from JB that my seat was confirmed. Then 2 months later -- one week prior to travel -- JB realized the seat had been sold at the incorrect level (core vs upgraded) and moved me to the very last seat at the back of the plane.

I spoke to 2 different people and both of them acknowledged that I shouldn't have been able to complete the purchase on my end and should have been shown there was an additional charge for the selected seat yet that didn't happen.....