Mid-May I upgraded from an iPhone 4 to iPhone 5s (refurb) through AT&T's website. Never had any issues with my iPhone 4 but the battery life was getting pretty bad so I decided to upgrade. I had a few phone ask me why I hadn't replied to their text messages and I never received them. Then I tried to text someone (non-iPhone) and the message couldn't be delivered. I restarted the phone and everything went back to normal for a while. This week, however, it's happened 3 times. I've had to restart my phone each time and then ding ding ding all of these unreceived SMS texts come flooding in. iMessage works fine. It's just the SMS texts. No issues reaching the people with a phone calls but texting just randomly stops working.
Any ideas? Should I go through the headache of returning the phone? Or is there a fix?
iPhone 5s, iOS 7.1.1, AT&T service and refurbed phone