If you had read the terms of the offer the deal was buy one Samsung get the S10e free, or $750 discount off another Samsung that is more expensive.
All buy one get one deals, or trade in deals are published on the website. It clears up a lot of confusion if you read the deals before you except the offers.
The terms of the offer would have been presented to you at the time of sale, in your receipt or by email. Did you read either the website or your sales receipt?