wcdma not working only 2g work

Very urgent,

My S4 I9515, phone is not connecting to 4g/3g, only connecting to 2g,

Its happened after - 1. change Imei (now not original Imei), because of country code

2. fall down 2 time

after one day of fall down, my mobile did not connect to 3g anymore . I checked every thing from setting.

What I did 1. reset factory setting.

2. software change 4.2 to 5.1 lolipop

3. change power cable

but still no working 4g or 3g,

please help me what should I do. technician also don't know. only say no repairing like this.

please tell me solution.