From what I can tell, the issue is likely (deliberately) confused by Toyota.
The box is fine, the filter is fine, the system as a whole is faulty. They've always got an 'out' on this - simply that the filter in use at the time of the ingestion of the dust was not genuine filter, and as such is not their product to warrant. Given that there is no way to prove what was in the car at the time, and there's no advantage to Toyotas overall sales income to be gained by paying for the fix, the problem will sit with you.
Your warranty is with your dealer however, supported by the importer. Suing the dealer, assuming the dealer did the maintenance - that may be a more promising avenue..
If you fitted your own filters, I don't see much opportunity to get anything back.
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