We are being asked for payment for a shower tray, which we have not received.

We cancelled the order, via phone, as we were told the item was out of stock. We obtained a credit for the said item, which the company actioned. We then purchased a shower tray from a different company. A year later, we are being asked for payment or the return of the shower tray, as the company are saying their supplier has proof of delivery. As we haven't received said shower tray, we have asked for proof of delivery, showing date, address and signature. This hasn't happened yet. Where do we stand legally?