HOW DO I GET MY NONPROFIT'S WEBSITE OFF THE BLOCKED LIST??

I have been trying for ages to get my nonprofit org's website (oceanmediainstitute.org) off the blocked list and released from being flagged as phishing or malware. Our site was once hacked (years ago), but we immediately took it down, fixed it and put it up on another completely new server with more protections. It is absolutely safe, yet some Microsoft users are still unable to access it. This is an enormous problem as it is preventing us from receiving grants and doing day-to-day business! I have contacted Microsoft several times with no response. I need this fixed urgently!