WotLK Character disapeared

[Brteeee]

For some time I haven't played WoW and didn't login into my account. I finanly decided to log in and play WoW for a while. After loging in I saw my account was cleared. No characters, no nothing.
I invested into those characters I had on my acc and now they're gone.
Is there any way to backup my account and return characters and items I had on them

[OhieMitzen]

If you played on Frostmourne S2 [April 15, 2021 - April 14, 2022]: Go to https://www.warmane.com/account/services select Frostmourne S2 and begin character transfer to Icecrown.
If you played on Frostmourne S1 [April 15, 2020 - April 14, 2021]: You should've transferred them to Icecrown when you had the chance. Transfers from Frostmourne S1 to Icecrown are now closed.

If characters are gone from other realms:
If they were below level 30, they were most likely deleted on inactivity cleanup. No restoration option.
If they were above level 30, and you don't have characters listed when you login, the chances are they were deleted by somebody who had access to your account. Either this was a "friend" or some random whom found out your login info. You can look for suspicious activity here: https://www.warmane.com/account/history.
There's a chance you may be able to recover one character for free via https://www.warmane.com/account/services by selecting realm -> Currency: Free -> Character Restoration.