Sounds like you attempted to d/l from the Seat official website, but you are in UK- am I right? UK Seat owners are advised to buy map updates from the dealership, however, there is at least one reliable source that I know of that sells up-to-date maps on sd card, and CD.

Are you using an sd card, or CD?
If sd card, there is a number towards the bottom of its label, which should look something like “6PO919866”. Can you confirm the card number, either by replicating the number on your card here, or upload a clear pic of it, and I will respond with a link for you to buy the correct card. Dont worry – whereas the dealership possibly quoted you around the 3-figure mark for the update, the site I use is half that – or less!