HOW TO USE YOUR CODE ONCE YOU HAVE IT - 04/04/2022
I had no problem getting my code from Samsung, but I couldn't make it work to subscribe. Fortunately I eventually found the answer, at least in the UK, but I suspect this should work globally.
(Anyone else succeeding with this answer PLEASE COME BACK AND SHARE if it worked for you, and whereabouts.)
SOLUTION:
Go to https://www.disneyplus.com/redeem and you will see you can enter the Samsung-issued code before you even log-in. Make sure you're logged out on the https://www.disneyplus.com site before clicking that redeem link.
You'll then be asked to log in or create an account. So long as your current subscription has expired you should be able to start a new one on your existing account.
If your subscription is still current, you must cancel it so that it does not auto-renew, then wait until the expiry date and then use your code to reactivate it from that link. Note the expiry date of your Samsung code that's in the issuing e-mail.
This worked for me, but to discover that (pretty obvious-looking) link above, I had to call Disney+ subscription on +442039362903 in the UK.
NOTES:
You can't renew using the Disney+ Mobile app. If you do, any code entry form is for the subscription partner (e.g. Google Play Store) and not Disney+, so the code is not relevant and is not accepted. This was my problem. By going directly to the Disney+ site at the address above you subscribe directly with Disney and the code works.
The regular Disney+ Web subscription page doesn't have anywhere to enter this code, so you need to do it using the link above.
I don't know why that link wasn't made more public.
Hope this helps you as I spent frustrating hours trying to solve this.
