In the footer of extstock:

© ExtStock 2017-2020. EXCHANGE CLOUD LIMITED. All rights reserved.

EXCHANGE CLOUD LIMITED is a cloud mining compagny in London
There is a lot of informations about them, and a number:

+44 7520638782
support@exchangcloud.com

https://exchangcloud.com/?a=support

I have archived their website and some informations, in case they rebrand their website.

Presure them, and sorry for you loss.