Other than notifying the telco about the matter, no there's nothing you can do

my office in bangsar south tower is using this device. It comes in pair so the main receiver is at the other end facing outer window. We have 4 pairs in my floor as the office occupied the whole 7 floors. So they put North south east west then the secondary device facing inside the office.

I forgot the name but the last i check per pair cost RM 2000++ and made in ITALY. It also has digital display for the signal. And guess what It has MCMC and sirim sticker on it.

So it's legal. Unless u dare to use china illegal repeater or booster RM 200 la

sometime it can be your phone problem as well..

some phone models are quite weak in signal reception..

u can try changing to other telco

Maybe the different telcos are using different transmission towers and/or transmit power and/or carrier frequency in your area.

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A 4G LTE cell tower can cover a range of up to 3 miles/5km for Internet data and 10 miles for voice calls/SMS. It's signals are line-of-sight = can be blocked by walls, tall buildings, hills, heavy rain, etc. It can only serve up to 60 users at any one time. 4G LTE cell towers are usually located in city areas(= more towers closer together) and along main roads and highways(= less towers in non-city areas) to cater for car nav apps like Waze.

So, if your phone is only receiving a weak 2 bars out of 5 bars in signal strength from U Mobile's 4G LTE cell tower when you are outside on the street(= your location is near the edge of the 3 miles/5km range limit), the cell signals will be more easily blocked by walls or other objects.
....... I live near a highway in KV = get at least 4 bars 4G LTE signal strength with U Mobile GX50 on my 4G Android device facing outside, ie not blocked by any house wall. In my bedroom = cell signal strength drops to 2 bars but still able to video-stream Youtube at 480p.

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Likely, the U Mobile 4G LTE cell tower serving your phone and house is located somewhere in front of your house. Install the Cellmapper app to see the actual location of the U Mobile 4G LTE cell tower.

How many bars of 4G LTE signal strength are you getting.?

HSPA+ is 3G = only about 1.5Mbps download speed. If you can get 4G LTE signals, you should also be getting 3G signals from the same cell tower. In this case, 3G only serves as a backup. In 2020, some countries will be mothballing 3G. In Singapore, there is already no 2G for feature phones.

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Try positioning your phone near an open window in your kitchen and 1st floor.

Looks like no solution to the problem of no mobile data at your kitchen and 1st floor. The problem should lie with U Mobile using only 4G LTE Band 7 = 2600MHz = higher frequency is more easily blocked by walls.

In comparison, Digi uses Band 7 and Band 8 = 900MHz = lower frequency is less easily blocked by walls;  Unifi Mobile uses Band 38/40 and Band 5 = 850MHz; and both Celcom and Maxis use Band 7 and Band 3 = 1800MHz.