Redeem Code function, Xbox Store

I purchased Fallout 76: Tricentennial Edition. The game cam with an Add-on code for the Tricentennial pack to be added, and a separate code for 500 Atoms.

I installed and updated the game from disc. No problems.

I went to the Xbox store, redeemed the Tricentennial pack code. "Code Accepted". Nothing downloaded. I re-entered the code, "code has already been redeemed". I check my Microsoft account - I own the add-on. I went back to the Xbox store, find the Add-on
"Tricentennial Pack", cant install it - no option to do so, UNLESS, I pay another £19.99.

Hard power cycle, uninstall, re-install, redeem on computer through account (code already used) checked the game menus, xbox menus its nowhere to be found as expected as it hasn't downloaded. I cannot download my add on anywhere.

I then redeemed the 500 Atoms code. No problems.

All the troubleshooting guides dont actually help, nowhere in the troubleshooting guides does it say 'redeemed code, download did not start, can't download.

Please can I have some insight on how to get the add-on for this ridiculously priced game.

Thanks in advance.

:)