FLASH 1voucher Gaming top up - complaint alleged pre-used PIN

Failed Instant online gaming top up from FLASH with 1voucher. The consumer lost R200.00 when uploading 1 of 5 R200.00 1vouchers. Pin reflected an error code with Used - invalid PIN. After contacting the FLASH, a screen shot was obtained from FLASH reflecting the other pin users name and the account name. That 1voucher was bought from a vendor who is part of a reputable chain Since then a further R450.00 has been lost./used bought from 2 other different reputable vendors. R200.00, R200.00 bought the same day and then a further R50.00. Question - How do the PIN numbers seem to be duplicated or uses? Does someone has access to the onetime Top up pin numbers? Re-print is not on all the till slips.