Hmm strange. I remember seeing in the fine print that the offer was only available if you signed up before a certain time when I did it. But I did the same as you, created a new Google account, then opened YouTube with the new account and I saw the offer. The one month offer you have seems to be the offer from YouTube and not from Samsung I think.
Maybe try to switch to your old Google account in the YouTube app, close the YT app, then clear the YT app cache, open back up the YT app and switch to the newly created Google account to see if the offer pops up. If it doesn't I guess you can also tap on your profile icon on the YT app, go to the settings and see go to Memberships to see if it shows up there.
