Messages only showing sending. how to fix?

[Parthiv Purkayastha]

My dad has an Intex Aqua Power Plus with Android KitKat 4.4.2. Whenever a message is sent, it only shows sending and later shows Failed To sent after a long time.and I can't receive some messages except few ones. I have done rebooting the phone and also tried force stopping it. Please help. How to fix?