In view of your situation for a long time, I need you to communicate with the school to see if they have posted your certificate.

1, may I ask first, is your certificate currently in school?

If you are at school, can you show it to me?

3. If I am not at school, where is my certificate?

If they don't let me see it, I can judge that your certificate has failed the exam or has been hung up.

When you go to argue with them, bring the agreement you signed at that time. If the two sides can't reach an agreement, you need to take legal procedures to protect your rights.