This transaction was done with the old chrome apps and my Ledger firmware is 1.3.1 - I have not updated the firmware in fear of completely losing my coins altogether.
Anyone got any idea how I can access/retrieve my coins?
No idea on how to retrieve them , if at the time you sent to that address your computer was compromised and you fed the adversary's address.
Could it be the case that you have sent
BTC to the address relevant to SEED + 25th word and now are trying to look on addresses pertaining to bare SEED, (or vice versa)?