As already stated... all the evidence leads me to believe that the seed mnemonic you have written down is NOT the seed mnemonic that generated the address you sent coins to. How or why you have a different seed mnemonic, I cannot answer, as I do not know what steps/actions you have done when setting up and using your Ledger.

It is also possible that you simply sent the coins to the wrong address (clipboard virus that changes addresses? or possibly just copy/pasted the wrong address).