I have ACM certificate which is associated with some other unknown AWS account

Hi, it could be caused by services such as API Gateway. Please check this reference https://repost.aws/knowledge-center/acm-certificate-resources. Depending on your use case (edge-optimized API or Regional API), the certificate could be associated with CloudFront or ALB. Please see if there is an API Gateway custom domain that is in use and associated with the certificate. If yes, please remove the association in API Gateway custom domain. Similarly, ElasticSearch Service can also create an ALB and associate it with your certificate. So please check if the certificate is associated with your resources including API Gateway, Cognito user pool, and OpenSearch. However, if there are no such resources that are using your certificate, please raise a support ticket so that the team can check the details.