I play on the steam version, when you go to the help section you get redirected the this email
marvelpuzzlequest@d3publisherofamerica.zendesk.com
after i got some cover swaps i got this email tho
Hello D3 Go! Customer -
We have updated our contact info for our customer support services and this email address is no longer valid. Please submit your support ticket directly in the game app or via email at support@d3go.com.
Thank you!
D3 Go! Customer Support
so maybe link to the correct email???