Did you enter the code in game? It has been a while but I think I remember having to add the code in game to actually receive it. Make sure that you redeem it on the shard you want the items on.
EDIT: Here is a link from UO's official Wiki explaining how to do it.
The King’s Collection – Ultima Online
''The King’s Collection is a theme pack purchasable from
Origin Store consisting of decor and furniture items for home owners. Special items are obtained by using the theme pack code in the ‘promotions’ section of the help menu after the code has been used to upgrade the relevant account in the
Accounts Management pages.''
"Entering the promotion code will place a token in the character’s back pack. When double clicked this token is replaced by the token box, containing the items pictured below in deed form, in the character’s bank box.
Be sure there is enough space in the bank box before activating the token"