Contacts for Genshin Impact players:
genshin_cs@hoyoverse.com
Contacts for Honkai Impact 3rd players:
honkai3rd_global@hoyoverse.com
Contacts for Tears of Themis players:
The customer help is actually in-game. To access it, tap on your profile portrait at the upper-left corner of the main screen to enter the Player Info page. Then, tap the "Customer Service" button in the lower-right corner.