Hi Laura,
Exam/certification issues are handled in Microsoft Credentials forum. There are support moderators over there that typically respond within 2 business days. You may use link below to ask your question over there:
Microsoft Credentials forum - Ask a new question
Depending on the issue they have the ability to have things fixed on the backend with your profile that may be preventing you from scheduling exam, certification(s) showing up, etc.
For what it's worth I take almost all of my exams at in-person facility. I know that may not always be possible, but I thought I would mention it since it seems to reduce potential problems. I have successfully taken online Pearson VUE exams as well, but majority I take at facility.
Please click Accept Answer if the above was helpful.
Thanks.
-TP