4g Cellular data for zenfone 3 ultral not working since 2 months ago

Hi,
I like my ZenFone 3 ultra very much since i bought it last October. But the 4g/lte (carrier is T-Mobile)stopped working since about 2 months ago. The speed now is only 2g which is very slow. Does anyone have similar experience and how did you resolve it?
Thanks.
Yong

Hi ...
Have you tried first ... Settings > Backup & Reset > Network setting reset ? We never know ...

Yes, i tried but didn't work. Do i have to upgrade my firmware or something similar? Thanks.

I just have unstable 3g work, mean speed is guud but connection is dropping each 2-3 mins what's not happening for 2g. Related for 2 recent 7.0 Android updates

Hi yongzhangNewYork,

Good day.
Are your firmware version currently on WW-14.1010.1706.50.
Did this problem happen even when you in the different location?
How often did this problem occur?
Please kindly try to try to use another different sim card for a check.

Thank you.

The firmware is up to date as you mentioned above. I tried to use SIM 2, but no data service at all. Had to switch back to 1. Its pity that it can not use 4g/lte network. Thank you for answering my question. 

It completely stopped working about three months ago.

Hello yongzhangNewYork
Please check that if your preferred network type includes 4G
You can access this page by going to settings>more>network settings
Thank you