Hi guys. I found my product on the third-party site . Written in support of hosting about this product that infringes copyright . They were asked to provide proof that this is my product. How can I prove it ?
You could give them a link to you item, and add some big item description likes:
Hi Mike (his name)! this is my fcking item, pls verify it! 
Exactly what else can you provide, on your item page there is also release date.
send them a DMCA
I did so , but they are asked to confirm.
Provide a link to your item(s) on Envato and additionally give them the contact link found on your items support page. Ask them to contact you through your support page for proof.
Confirm what?.. in a standard DCMA there is all the info to prove the file is your