Hi Eric,
Thank you for contacting the Microsoft Community.
With the event that you have completed, you should have claimed your discount 5 business days after the event has concluded.
You no longer need to wait for a voucher to redeem your free exam since Microsoft now offers a ‘voucherless’ discount that you can claimed by linking your personal and work/organization accounts when scheduling.
Meanwhile, please note that your exam discount will depends on what event you have completed, please see details below:

Since you mentioned that the offer assigned to you in error, please send us a step by step screenshots using Problem Steps Recorder (PSR) and start the recording from the time you're signing in until you encountered an error message.
You may upload the PSR along with the requested information via private message (refer on the image below):

Once we have the complete details, we’ll verify your profile and escalate the case if needed.
For more information, you may watch this instructional video for the steps on how to link your accounts and redeem the offer.
I look forward to your response. Please note that if no response is received after two business days, the case will be closed and locked. After the case is locked, we will no longer be able to respond, even through Private Messages. Thank you.
Best regards,