Understanding trade in payoff
We traded in a phone for an IPhone 12 and was told we’d owe $300 difference. We wanted to pay that off but were told they would bill us $10 a month for 30 months. That was the difference between the costs of the IPhone 12 less trade in value of our old phone. So, 10 months have rolled along and we’ve made 10 payments at a net of $10 each for $100. Now, we’re looking at the IPhone 13 but was told that we have to pay off the IPhone 12 at 20 payments of approx $30 each instead of paying off the 20 payments at $10 each . If we only owed $300 to begin with, and have paid $100 so far why would we owe the $600?