Like stated above, accounts automatically get removed/deleted from the servers after 18 months (last time I checked), so it is very likely that this happened to your old account as you stated 'I haven't played on this account for years'. Raz also did a sweap of accounts around the time Registration Maintenance was complete, and the username instant change/delete features were added, but I doubt your account was sweapt with those due to you using the plural 'years', being more than one.
However, if you're wanting that old account back, you will need to wait until the next Registration opening. UNLESS you cannot wait/do not want to wait, in that case, you can change your current username, or the username of another account that you might still own. Here's how, and some things to note of course:
▸ Return to the FeralHeart Homepage and click on the 'user panel'.
▸ Login as you normally would on the account you're wishing to re-name.
▸ Locate 'Change Username' and enter your new username and then enter your current password in the box below to confirm the change. As mentioned above, the symbols a-zA-Z0-9_+-.,!@#$%&()?=`{}[] should not give you any issues. (If it doesn't work, try again but without using any symbols to see if it changes anything in terms of success).
▸ If all fails, send an e-mail to [email protected] using the e-mail you registered that specific account with. The contents of the e-mail should include your old username, and the new username (the one you want it changing to). Any other messages sent through that e-mail will not be answered. If you need a little added help, send the e-mail and write "[current username] to [new username]" as that is more specific and helpful.
I am not sure what happens beyond that stage, but I'd recommend waiting patiently for 48 hours once the e-mail has been sent, as it shouldn't take longer than that for a responce. Just be sure to check your e-mail often.
If you need any further help or have any questions regarding, then I will be back to check up on this thread.