Most Likely Due to a Violation of the Yahoo Answers Community Guidelines
Check the Rule Book to see what you may have Done wrong if After Reading you find you did nothing
Wrong then Appeal use the Alternative Appeal Form
If you got a Violation Email Notice dont use the Link from the Message that one is not working
Correctly you will get a Error message saying it did not come from your Account
Go here to Appeal
https://io.help.yahoo.com/contact/index?page=contact&locale=en_US&y=PROD_ANSW
Click on Contact a Yahoo Specialist then Appeals then Follow the Instructions from there