Are you sending with Australia Post? If you open an enquiry with AP shortly after it's missed the AP delivery deadline, they seem to pop back onto the radar after a few days based on my recent experiences.

AP aren't scanning much due to parcel volumes. Once scanned in at lodgement, most of mine don't get another scan until the day of delivery.

Best thing you can do now is manage customer expectations. I was already messaging any buyer once I've posted an item, and now I include a sentence or two about current delivery timeframes.

I've had a couple of recent parcels delivered very late but received glowing feedback as the buyers appreciated my efforts to keep them informed. When life gives you lemons, treat your buyers to lemonade!

If you're not sending with AP, I apologise for my mostly irrelevant reply.