@Emre hey, thanks for your question and welcome to the community!
Have you followed list health best practices before sending your email from Klaviyo?
Normally Klaviyo will flag a new account when they are trying to send emails to an uploaded list for the first time, following which the Verification and Compliance Team will manually review the flag and make a decision on the account.
You can then sift through THIS ARTICLE to help troubleshoot a particular condition that wasn’t met, that would’ve caused your account to be disabled.
Sending an email to Klaviyo support should help you uncover exactly what was the exact reason for this happening.
Good luck, and I hope this helped!