Simpliest way to look at shiznit
You agreed to pay them for one yearof cover. They agreed to let you pay it monthly. Therefore, you owe them the whole amount, plus interest for monthly payments, plus whatever they may charge for administration.
If they transferred the insurance to you new car, then the policy continues, (unless they inform you of changes), same as if you had a fender-bender, got it fixed and carried on.
It is something you really must discuss with the insurance people, just to be absolutely sure that you have insurance and exactly how much you owe.
Been there, done that, got the T-Shirt, and took a bath in it.
Old Salt