Multi-AZ error billing

I followed this link https://aws.amazon.com/getting-started/hands-on/create-mariadb-db/ to create and host my MariaDB on this platform, but even know I selected the free tier and disabled Multi-AZ deployment by selecting "do not create stand by instance", I was still charged $89, most of which are name: '$0.342 per RDS db.m6i.large Multi-AZ instance hour'
'$0.2 per IOPS-month of provisioned io1 IOPS for Multi-AZ deployments running MariaDB' '$0.25 per GB-month of provisioned io1 storage for Multi-AZ deploy'

Furthermore, under the configuration page, I can see that the value for Multi-AZ is no, according to this link https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Concepts.MultiAZ.html For Multi-AZ DB instance deployment characteristics, I only meet the first two characteristics, the third one, "The value of Multi-AZ is Yes." which does not apply because of the above. And the Multi-AZ DB cluster deployment is unrelated at all to my case. why was I charged for a service I did not select to begin with?