Default WiFi Not working while I'm not using the Phone

Hi experts,
I have downloaded the OTA from Verizon. Please find the attached picture of my Phone, to know the Technical information

MY Problem :
When, I'm not using my Phone, even though, I'm at home and I have WiFi at home, My phone is disconnecting from the WiFi and using the Cll 4G LTE Signal, after I lock my phone screen.

This is the 3rd month in a row, I'm paying insane charges for the Data. Did anyone found a solution for the problem??


Thank You.
Attached Thumbnails
Click image for larger version

Name:	Screenshot_2014-04-23-22-41-55.jpg
Views:	26
Size:	33.0 KB
ID:	2805646