1) Check your DNS registrar and make sure there are no new subdomains. dnsdumpster can also help a bit.

2) Check for any new files in the directory tree of public facing sites.

If you're sure all is good you just have to keep escalating with microsoft and creating new requests to remove your domain multiple times a day from different IPs and emails so you can land in the right queue eventually. Squeaky wheel and all (don't forget social media noise).