Network not changed from 3G to 2G on Xperia L

I am using Xperia L, If i used 3G connection in one place then i moved to other place if 3G connection is not available means my phone not changed to 2G connection, i set network setting mode is WCDMA/GSM. In that time if any one called to my number its says "not reachable" what i do please help me.

i am using

Phone Name : Sony Xperia L C2104

Android Version : 4.2.2