Did it work before?
When did it stop working?
By "messages" do you mean text messages?
What happens when you try to send a text?
Can you receive texts?
Can you make/receive calls?
If you mean MMS messages then you need cash credit on your account to pay for them.
See here:
If you need to contact 48 support about this then see the link in my signature below or email them at support@48months.zendesk.com
