I played this game since the beginning and the support team NEVER managed to solve the chat issue for me. However I found out why and how to solve it after 9 months of playing this game. There is obviously a network blockage, perhaps due to their network coding or setup.
Just install the “Free VPN” software (available for both iOS and android) and play the game with VPN enabled. It should solve your chat issue. Hope this helps and have fun.