iPhone on us (April 2021) trade in now

So I traded in my iPhone 11 for an iPhone 12 back in April. Since then I’ve been receiving monthly bill credits that’s paying off my phone.

I was wondering if I can trade in my iPhone 12 to Best Buy for a 13 pro? To my understanding I just can’t cancel my line or else I pay the remaining balance. I don’t necessarily have to keep the phone for 24 months?