I had a similar problem with a Lowrance unit, they didn't want to honor the 1 year warranty. It was posted on the Lowrance website that the unit had a 1 year warranty, when presented them with the facts they repaired my unit free of charge. It looks to me that Humminbird Carrie's the same warranty, does not say cannot buy from Ebay.
https://www.humminbird.com/support/warranty

As they say Never give up! Hold your ground, they have no out in this