If you think that someone has accessed your Tradeit account, please complete these three steps to protect your account:
Change Steam password: Head to your account settings and click "Change My Password".
Deauthorize all other devices: Open Steam Guards settings and deauthorize all devices. This will log you out of all devices, except the one you clicked on the button with
Revoke your Steam Web API Key: Open the Steam API page and revoke your key. You do not need to create a new API key.