Hello, with the given description you have given, your account is most likely compromised. Please do the following to regain control of your account:
1. Change password immediately and change it anywhere else you have the same password set. The scammer will try to log into your email with it when he loses access.
2. De-authorize all other devices here: https://store.steampowered.com/twofactor/manage
3. Revoke any API keys set. Their only use, if you don't know what it is, is keeping control of your account. https://steamcommunity.com/dev/apikey
Once you have done so, please reply here so that we can continue with the report.