Let me ask you a question. If Christ pays the debt of your sin, what is left to pay?
Let's think of a bill at the grocery. Your bill is 232.87.
Jesus steps in and hands them cash (no checks or IOU's from the big guy). You're covered. Everytime you sin and repent, he steps in and pays the bill. If there's nothing on the register, how can you owe anything? If you walk out of the store with your paid for groceries, are you stealing? Is the food less nutritious because he paid for it? More?
I mean I could ask you a lot of things here, these are pretty obvious. If purgatory was necessary to our faith and
the covenant was sealed by Christ, why do you suppose there isn't a single entry in the entire new testament mentioning it by name? Not one. Why do you suppose Orthodoxy never heard of it. If orthodoxy is part of the church and never taught this or unum sanctum, etc, who do you think was in error for teaching or not teaching these things. Does God arbitrarily just change the covenant? No. Somewhere in there is an answer for you - which you seem already to instinctively know. It isn't scriptural.
I said, I've never really been attached to, or detached from the concept of purgatory. And your grocery bill analogy, when juxtaposed against the 1 Corinthians passage I cited from my catechism, is not persuasive at all. I remember fr. guido sarducci postulating something very similar.