Oh... so you had 3 accounts in Freelancer account manager.
Now you only have 1 in Freelancer account manager?
Freelancer account manager saves accounts to .ADF files.
Try "accounts > import from file" on all the .ADF files you can find, using Freelancer account manager.
If you have windows I suppose you could use a file search to find *.ADF in case you have misplaced the ADF.
You can also add account IDs manually "accounts > Manually add account" and then type in the code you wrote down.
If you have lost the other two account codes though, I'm afraid there's nothing you can really do besides PMing an admin with all your shipnames and asking really nicely and politely.
Sorry I can't help more.
EDIT: for future reference. YOu can use "accounts > export to file" then select "export all" to save all of your accounts to a single .ADF which you should save on a USB or a CD or something to keep it safe.