My thought, being from the US, and not a lawyer:
If you have a copy of the original contract, look at it and see if you licensed the images to the owners or the business. If the business, I would assume the license travels with the business, assuming they didn't re-incorporate as an entirely new business. If they re-incorporated as an entirely new business, than I would consult a lawyer on if it voided the previous contract or not.
Now then, it may not be too late to salvage the relationship. You may just want to call them up and say that the first invoice was sent by mistake.
Another thought would be to see if they plan renovations or anything of the sort. Then offer to license for free the current images and then shoot (for your normal rates, obviously) everything when their upgrades are complete. By my understanding, you aren't really losing anything financially, as the original fees you received would have still been covering what you would have been compensated had the original owners not sold. But instead, you now stand to profit with a good working relationship and possibly good word of mouth marketing.