Why does my UK tag change show as complete but the domain is not in my account?

A UK domain transfer is a 2 stage process. You need to:

Change the tag to STACK
Transfer this in through the Greeny Host Host control panel
The best way to check the current tag for a domain name is via the Nominet WHOIS system. Once you’ve confirmed this is using STACK, complete the transfer following the steps below:

Login to your account and click Transfer a Domain
Enter the domain name and click Search.
Add the domain to your basket and complete checkout.
The transfer will complete almost instantly.