I have a prepaid unlimited texting acct. on my iphone 5s. Has been connected and working great for over a month now. As of yesterday I can no longer send or receive text messages unless I am connected to wifi. I have never had a problem sending or receiving text messages until yesterday. I have automatic top ups and last payment went through this week so it's not because I haven't paid my fees. What could be the reason for this and how do I fix it?