It seems odd that there is a requirement for www.blog.vizergyit.com when all we are concerned with is blog.vizergyit.com. They state this is a Let’s Encrypt requirement, but I’m not so sure. Can someone confirm?
As @JuergenAuer pointed out your host is misleading you. This isn't a requirement from Let's Encrypt, its a requirement of SiteGround's own ACME implementation
I don't know why they are telling customers that this is a Let's Encrypt requirement. You aren't the first person to come to the forums with this particular issue. If you have the chance, please provide feedback to your support agents that they are providing inaccurate information so that hopefully the agents can be educated with the correct answer going forward!
I have been battling with SiteGround off and on for months concerning this. The initial verification works without the WWW DNS record, but the renewal will sometimes fail eventually causing the Let’s Encrypt cert to expire. Their answer has always been that the WWW record is required or it may not work and that it’s a Let’s Encrypt requirement. I agree that they are spreading poor information to their customers and making things more difficult than they should be.