Unauthorized Access on Skinsmonkey Trade Despite Steam Guard

Just had a skin trade on Skinsmonkey, but even with Steam Guard protection, someone managed to get into my account. The trade was redirected to an unfamiliar individual, and unfortunately, I fell victim to a scam. I have no association with this individual, and I am the sole keeper of my password. It's evident that Steam's security measures are insufficient in preventing unauthorised access. I require help as I find myself in a difficult situation.