Having trouble using my Mix3 with canadien sim card

Jan 10, 2019
I am in Quebec, Canada now and bought my Mix 3 from China. I can only use 2G data with any of the local sim cards, while 4G+ with my chinese sim card.
Having no idea why...

I tried to flash an EU Rom but it kept reporting "can't upgrade from an unofficial Rom package". But the Rom package was downloaded from here.....

Need help plz....