To turn off contacts, go to Settings > Mail, Contacts, Calendars then select the mail account and turn of Contacts. Restart your iPhone and then turn Contacts back on. You can go one step further and delete the email account then re-add it again after a restart.
I also frequently perform a complete restore when an iPhone is particularly troublesome. Remember, this process completely erases your iPhone and returns it to factory default. Make sure your apps, music, pictures, etc. are synced to your computer.
1. Turn your iPhone off.
2. Connect one end of the USB cable to your computer (do not connect the other end to your iPhone yet.)
3. While holding down the home button, connect the other end of the USB cable to your iPhone.
4. Continue to hold down the home button while your iPhone starts up.
5. Eventually you will see the iTunes logo. Your iPhone is now in recovery mode.
6. Open iTunes and click on Restore iPhone.
7. After restoring, set up as new iPhone
8. Setup your mail. Sync music, apps, pictures etc.