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Are you referring to an exam you took in September 2025?
Did you create a case at the time. If you didn't I am not sure what can be done after so long.
You can only reschedule with more than 24 hours before the exam and not after.
Also, It is unlikely that the voucher will still be valid as they generally are only valid for 90 days.
Try support https://aka.ms/CertificationSupport