Are you a dual citizen? If so until you revoke your US citizenship you are supposed to file a US tax return FOREVER and no matter were you reside or what other citizenship you might hold.
WBEN-8 forms are for non- US citizens who reside in countries that have a tax treaty with the US (includes Canada and many other countries). This would exempt you from withholding taxes.
When properly documented, dual citizens can avoid any double taxation.

"What else could I do? I had no trade so I became a peddler" - Lazarus Greenberg 1915
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