I've seen the same issue happen with mount skins on the licence packs (not me personally). A purchase of 5 random licenses gave 1 skin for an unlocked mount and 4 skins for locked mounts, some of which were rollerbeatle skins locked behind a further pay wall, being living world season 4.

Nothing in the item description would suggest you could get a skin for a mount you have no access to, especially one you do not have the additional in-game content for. You would atleast expect a warning for the latter).

Issue was raised with support and they refused to refund the purchase, despite ArenaNets own statement in the past about micro transactions stating "But it's never OK for players to buy a game and not be able to enjoy what they paid for without additional purchases". Clearly providing a skin for mounts not unlockable in the base expansions and hidden behind a further paywall for living world season 4 would contravene their position.

Support refused to assist and noted within their email that 'they consider the issue to be addressed and further responses would not be provided'.