Hello, Francesco.
Thanks for reaching out to us, here at Microsoft’s Community.
As we understand from your post, you took an Exam with Certiport but cannot see it in your Dashboard and would like to Merge both Accounts.
Please know that when it comes to Achievements earned through Certiport you may download it, along with the Badges, through Certiport’s page.
Once you go to their website, follow these steps:
Log in and choose the Organization Administrator role from the drop-down menu.
Select the Reports tab.
Click Print Certificates.
Select the program you wish to print from the drop down box, or select Any Program.
Select the date range. You may print certificates within 1 year after the exam was taken. Click Search.
All available certificates will display. Check the box for the exams you wish to print, and click Print Certificates.
Use the options within the PDF window to print or save a copy of the certificate.
Your Certificates and Exams can also be found on your Transcript, which can be downloaded through your Microsoft Certification Dashboard. It may be used as a proof of accreditation as well.
We have started a Private Message where we would request some details about your account to complete an evaluation process. You can access on the top right corner of this page, as shown in the image below:

We look forward to your response. In case we do not receive an answer within two business days the thread will be closed and locked and you will not be able to reply through either channel.
Best regards,