if mail.zenlife.bg points to a server other than the cPanel server you're issuing the certificate from (as it appears to be), you'll want to uncheck it when issuing the certificate.
I'm not too clear what you mean by this.
If changing the IP in Cloudflare to your new server causes the wrong website to load, you won't be able to issue an SSL certificate in cPanel. There's not really any way to work around that. The site needs to work first.
You may find that the solution may be to temporarily suspend Cloudflare and point your domain to the new server, then issue the certificate, and then revert whatever changes you need.