Check Spamhaus, and go through their delisting procedure if necessary. https://check.spamhaus.org/
Once delisted there, you should start being able to send to yahoo again within a few days.
You might also review their deliverability expectations:
https://senders.yahooinc.com/best-practices/
Optionally, contact their support directly, be prepared to explain what specifically you’re doing to stop future compromises.
https://senders.yahooinc.com/contact/
