Hello Khaled73,
Welcome to the community!
Is your phone the Sony Xperia Z3 D6633? If it is, these are its band/frequency specifications:
| 2G bands | GSM 850 / 900 / 1800 / 1900 |
| 3G bands | HSDPA 850 / 900 / 1700 / 1900 / 2100 |
| 4G bands | LTE band 1(2100), 2(1900), 3(1800), 4(1700/2100), 5(850), 7(2600), 8(900), 17(700), 20(800) |
That phone would have all of the compatible bands/frequencies for 2G and '3G'. With regards to LTE, that phone would have three of the compatible bands/frequencies.
Since the phone is capable of LTE, it should be using ltemobile.apn You can verify the correct settings here.
Hope this helps 
Cheers
