Thank you for your reply.
If there is no issue with your SIM card provider (paid bills, contact issue, locked to network etc.), the next troubleshooting step will be to restore your phone.
1. Download and install iTunes on your computer. Check the link below to donwload iTunes - click here
2. Plug your iPhone into your PC or Mac with the USB cable (SIM card needs to be inserted).
3. Press and hold the power button at the top and then slide to power off the iPhone
4. Press the power button to power the iPhone on and keep it held while simultaneously pressing the home button
After a few seconds a yellow alert triangle will appear and the iPhone will say it is iPhone Restore Mode.
5. Open up iTunes and click on the Summary tab
6. Click on Restore to restore your iPhone. This will reset all your iPhone's setting to the factory defaults.
If you don't have backup created here is a procedure how to create it.
1. Download and install iTunes on your computer.
2. Connect phone to computer via USB cable
3. Select your iOS device in iTunes under Devices
4. Right-click (or Control-click) the device and select Back Up
Please don't hesitate to ask if you have any difficulties. I will be happy to help with any follow up questions.If you have any difficulties or you need more information please do not rate my answer negative BAD service or POOR service. Reply to me using "Reply to Expert" button and I'll provide you with more help.