Hello, good day and thanks for your question. Sorry to know about this and I understand that you have redeemed a cape in Minecraft but it has still not reflected on your account.
There are instances that there will be delays with regards to the distribution of this but you will also need to ensure that you have redeemed it on the correct account.
If it has been more than 24 hours and it is still not on your account, you may now check this with the Minecraft team at https://aka.ms/Minecraft-Support/ for your account to get checked and hoping that the cape/s will reflect on your account afterwards.