Might happen the mycloudnas.com portal is blocked by some commercial Web content control system. If set-up corrrect, any other well-known DDNS domains (dyndns.org, no-ip.org, ... should be blocked, too.
Is the problem just to access the MYCloudNAS.com portal (www), or also when resolving direct to your NAS/router by connecting ie. http://[yourname].mycloudnas.com:8080/ for example?
MyCloudNAS is not an access control system - the simple access system on the www.mycloudnas.com portal is just in place to hide the services available to avid the system is abued to discover ervices available.
[yourname].mycloudnas.com does connect direct to the NAS (resp. the router WAN public IP address) - just like any other DDNS system.