Moral dilemma

Petriix

No dilemma. If you've made a reasonable effort to inform them and have appropriate evidence to convince a judge so 'on the balance of probabilities' then there's nothing to lose and plenty to gain.

I'd ask for a refund of the credit balance and hang on to enough cash to pay for a year's worth of supply. They can't legally bill you for longer so, if it drags on, your win increases but your liability doesn't.

In all likelihood you'll have to pay a reasonable estimate for the past year's supply from whatever point they issue an an accurate bill.