NEED HELP ASAP (REFUND)

So I got this email from the website I'm trying to refund (Y3 Yamamoto) and my refunder isn't responding anymore and it seems he won't help me with it, I don't know what should I do and I don't know what he told the company when he called but I'm assuming it was the never received item shit, so can anyone tell me what should I respond to the email?

This is the email:

Thank you for contacting Y-3 Online Store.

We are sorry to hear you have not received your order *****...

Our courier confirms your package was delivered on 07/12/2017 at 2:22 P.M. in **********, and Left At: Front Door.

As the package appears to have been delivered, please check if someone at that address (such as a nearby-resident or a building manager) has received it for you.

We have already notified our assistant at UPS, who will perform an investigation.

UPS investigations usually take at least 10 working days. We will contact you again as soon as we have more information.

Please do not hesitate to contact us if you need further assistance.