International phones are built to a MUCH lower standard of quality. I was taken on once by one, was able to get my money back thankfully... The LED light was about 1/10th the brightness of a US version Samsung, the processor was a LOT slower also... (This was a Note 4 phone that this happened to me on)...
It is more likely that you were sold a knock-off piece.
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https://www.frequencycheck.com/compatibility/vqzE0/samsung-sm-g9600-ds-galaxy-s9-duos-td-lte-cn-samsung-star/countries?utf8=%E2%9C%93&q%5Bname_or_code_or_keywords_cont%5D=Usa&commit=Search
It is more likely that you were sold a knock-off piece.
almost true
Thank you!