Hello, good day and thanks for your question. Sorry to know about this and I understand that you have encountered an issue with the arrival of your redeemed Minecraft cape.
After checking the above and to add to this, please take note that there might be delays specifically when there are other players worldwide which is doing the same thing and if it still has not arrived then you can also reach out to the Minecraft team at https://aka.ms/Minecraft-Support/ for your account to be checked as well.