There was no misconfiguration, just millions of DNS requests but not millions of actual users. I was in contact with AWS support multiple times. The only solution was so use AWS Shield Advanced. They did refund most of the charges but it was too risky for me. Even after I moved DNS provider there was DNS requests to the R53 zones. I can highly recommend https://dnsimple.com though.
There was no misconfiguration, just millions of DNS requests but not millions of actual users. I was in contact with AWS support multiple times. The only solution was so use AWS Shield Advanced. They did refund most of the charges but it was too risky for me. Even after I moved DNS provider there was DNS requests to the R53 zones. I can highly recommend https://dnsimple.com though.