Handling time not working - please help

I’ve had a custom listing up for just over a month.

I had the handling time set to 12. Everything was fine, the two orders we’ve had showed appropriate send and deliver by dates.

I was checking the listing in the search results and realised it had changed to deliver by Tomorrow. I raised a case and was told:

I understand that the ASIN : B*is showing in the search results as delivery tomorrow even though the handling time is set to 12 days as this is a custom listing.

I would like to inform you that, showing delivery dates on the website are automated process and there is no manual intervention on this delivery date process.

An order has now come through with a ship by of today and delivered tomorrow.

I’ve closed the listing now while I figure this out, but does anyone know how to fix this?