Based on what you've described, it looks like you have duplicate records (two Cisco ID's) in the Certification Tracking System and that might explain why you are having difficulties using your Networking Academy exam discount voucher. To have your duplicate records merged, please open a case with the Certification & Communities Online Support team and one of the agents will be able to assist. Once the records have been merged, you should be able to use the voucher.
If you have concerns about the ICND1 voucher itself, you might try reaching out to your instructor or Networking Academy support (as Ing_Percy suggested) so that they can verify if the code is for the correct exam.
Cisco Learning Network Moderator