For anyone like me that has CUN-L21 and had problems with B115 , the likes of : voip apps not working (facebook messenger , not the lite one , whatsapp , viber) , apps that use camera not working , even shazam ; here is the solution to go back to something else:
Take the B123 firmware from here (the SD update one) :
http://huaweidevices.ru/
Extract from it the update.app
Extract update.app with HuaweiUpdateExtractor
Move resulting system.img to adb folder on PC
Plug phone to USB , reboot to fastboot
Open CMD in ADB folder , type fastboot flash system system.img , wait for it to finish , fastboot reboot
Done
Now all the aforementioned apps are working , sim is also working , all is good. Wasn't rooted but i just flashed supersu and it's rooted again.
Hope i helped someone in need who had problems with b115 on cun-l21.
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EDIT : there is a working flashable rom here :
https://xdaforums.com/android/help/rom-emui-3-1-huawei-y5-ii-lxx-hwcun-t3589057
I flashed that through TWRP and everything worked perfectly except the sim was not recognized , so i had to find the different solution from above.
But i was thinking if the meta-inf folder from that zip can be used in future projects of rom porting that we may have.