What error message do you get when you try to send a text? Do they send successfully to any contacts at all? Did it ever work? You seem to be using an iPhone - are you sure it's not some issue with iMessage that's causing this problem? If none of that helps you'll probably need to contact 48 support for more assistance. See the link in my signature below.
Hope this helps.
I am not a 48 employee so if you need to contact 48 support then use option 3 or the chat facility here.