Sounds like this. That website is totally fake, it still has a Christmas page and most buttons do not work. There have been websites mimicking Royal Mail to fish for details by mass texting. This one starts by asking for your post code, then tries to get you to pay for a redelivery fee which Royal Mail never ask for. Obviously get you to put in your card details and you can guess what happens next..
I do not believe Royal Mail send texts for deliveries? They do leave the cards.
Seems like this isn't related to the order you recently placed.