Dear olimaniac, your account is suspected by Steam Support for violation of the Terms of Service Agreement.
Steam Support Service found that you were dealing with third-party sites and decided to permanently block your Steam account. Account functionality will be limited, the possibility of transfer or sale of items from the inventory will also be blocked.

The restrictions will take effect within the next 2 hours and cannot be removed or appealed. If you want to save your valuable ingame skins, we allow you to transfer them to another Steam account. Regards, Steam Support.

More info on this topic is available here: Steam Terms of Service Agreement.