Outlook.com S3150 block: olcsupport form returns "Error submitting case" - is there another way to contact the deliverability team?

Hello,

Our mail server's IP is being rejected by Outlook.com / Hotmail / Live with:

550 5.7.1 Unfortunately, messages from [x.x.x.x] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150).

We have fixed the likely cause on our side and want to request mitigation, but the Sender Support form at olcsupport.office.com fails every time. After pressing Submit it shows "Thank you - your request was submitted. Error submitting case", and no case number or confirmation email ever arrives. We have tried several times, from different networks and with both a work and a personal Microsoft account, with the same result.

Questions

• Is the olcsupport form currently having problems, and is there a known fix?
• Is there another way to reach the Outlook.com deliverability team to request mitigation for an S3150 block (for example an email address or alternative form)?
• Is delist@microsoft.com the right contact for S3150 consumer blocks, or is it only for Microsoft 365 (5.7.511) blocks?

We'd prefer not to post our IP publicly, so a private route would be ideal.

Thank you.