Hello Vimalfromahmedabad,
Thanks for connecting with Apple Support Communities. You've completed some great troubleshooting steps so far.
To clarify, do you experience this issue with the Contacts, Phone app or both? Using these steps to close them may help:
1. Double-click the Home button to show your most recently used apps.
2. Swipe right or left to find the app that you want to close.
3. Swipe up on the app's preview to close the app.
More details found here: Close an app on your iPhone or iPod touch
If the issue persists, we recommend that you contact Apple Support directly. Depending on your region, you may be able to contact them here: Get Support
Best wishes!