Have you checked the settings in the app settings for your mms ability? The provider would be my next call if this phone never had this problem before.
It would help if you also tell us which device you're using. On Samsung devices you can check this option in the Apps section in your phone's Settings, tap the menu button and select Special Access. There you should see a 'Use Premium text message services' section where you can turn on/off access for registered messaging apps.