Negatives usually are working — the traffic you are still seeing comes from close variants, from a different campaign that has no negatives applied, or from reporting lag. Negative exact only blocks that precise term, so plurals, misspellings and word-order changes still get through unless you use negative phrase.
The three real causes
Close variants: Amazon matches plurals, misspellings and small variations. A negative exact on one spelling leaves every variation live. Negative phrase catches the family.
Wrong level or wrong campaign: a negative added to one ad group does not apply to the others, and the spend you are seeing may be coming from a completely different campaign targeting the same term.
Reporting lag: search term data is delayed and sales are attributed up to 7 days after a click. Spend appearing today may have happened before the negative existed.
How to confirm which one it is
Pull the Search Term report and add the campaign and ad group columns. If the term appears under a campaign you did not negate, you have found it.
If it appears under the same ad group but as a slightly different string, it is close variants, and the fix is negative phrase rather than negative exact.
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