Hey!
It's possible that either your privacy settings are messed up or that you are shadowmuted. Shadow mutes are a type of punishment issued by Microsoft for chat-related behaviour. When you are shadow muted, your message will get sent but other players will not be able to see it. A shadow-mute will follow you between featured servers and Minecraft Realms. Team CubeCraft is not able to help you with this form of punishment, as they are done automatically by Microsoft systems. The only way you can lift this type of punishment is by saying nicer things in chat - this will improve your reputation, and can result in the mute being lifted after a while. Keep in mind that spamming things in chat (such as the alphabet) will not result in your shadow mute being removed - this is against CubeCraft rules, will worsen your Xbox reputation, and can actually cause the shadow mute to be extended, or even made permanent. Shadow mutes are separate from Microsoft privacy settings, which can also prevent you from seeing chat or sending messages. You can check
this thread to see how to change your privacy settings