CeX says my item is dispatched, special delivery, but Royal Mail just says come back later.

I ordered an item worth over £150 from CeX on Saturday 24th, on Monday they said they'd dispached it and gave me a Royal Mail number. When I try and track my item on Royal Mail, it just says please come back later. Have CeX actually dispatched it? Special delivery is guaranteed 1 day delivery so I was expecting it today (26th) as it was 'dispached' yesterday! Anyone have this problem or know what's happening?

Thanks.