Hello Sanika,
Thank you for contacting the Microsoft community.
Missing your PL-300 exam due to technical issues on the OnVUE application as during your exam appointment, it got stuck and crashed which resulted in you being unable to take the exam and as you try to reschedule your exam, the company voucher was not reinstated. Allow me to offer guidance on how to navigate this situation effectively.
For us to verify your profile and check this for you, please share the information requested through the private message that I initiated. This will allow us to verify your profile.
Normally, for issues during the exam, it is best to contact Pearson VUE directly and request assistance in rescheduling your exam. Meanwhile, since you mentioned that you used a company discount, it is best to reach out to the Enterprise Skill Initiative support team and as they are the ones with the specialties to deal with concerns and issues faced by ESI learners. I have provided their contact details on our private message.
To access the private message, please click the message icon under the "Question Info" as shown in the image below:

Note: Pearson VUE and ESI support responds within 3 to 5 business days via email.
Furthermore, as per the OnVUE Page, before scheduling an exam it is best to ensure that your testing space and your system and network are within the requirements. Running a system test prior to the exam can minimize the possibilities of any technical related issues and reviewing the OnVue Technical Requirements.
We are doing our best to make your experience better and we would love to hear your insights by submitting your Feedback and Complaints online as this will help us and our exam delivery providers to improve your experience.
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.
Kind regards,