I can't send messages on anything connected with Xbox one or pc app or phone app etc.

Yes, and yes.

The Xbox itself, Xbox app on mobile, and Xbox app on PC are all connected in terms of messaging, so sending/deleting a message on one of those platforms affects what you see on all of the others.

There were two apps in the google app store, an xbox app and an xbox beta app. the beta one crashes when selecting messages or it just says something went wrong and doesn't display any messages. I tried using the other xbox app and
that seems to be sending messages ok (using a pretty old Samsung Galaxy 2 tablet so I can understand having issues there). On the desktop pc I can send messages on xbox.com but I can't tell if they have gone through because my message history on xbox.com isn't
updating so I can't see what I sent, I have to go onto the app to see if the message was sent. the windows 10 app works fine for everything apart from the messages, when I click on the message icon the app crashes.

Visit https://support.xbox.com/es-MX/xbox-one/xbox-live/cant-send-messages

Hi have you tried signing out and back into the account? Sometimes it's just a glitch

Hello!

Thanks for reaching out to us here on the forums with this situation. I understand you're having issues with your messages not sending on your devices. Have you taken a look at

Xbox One online safety and privacy settings. Make sure in your privacy and online safety settings are set to allow communications. You can also do it from your console's "Settings' under the "Account" go to the "Privacy & Online Safety". Xbox Live Settings
then where it says Communication. Make sure sending messages is enabled.