This is a scam but your account is compromised. Do the following steps to secure it:-

1. Scan for malware https://www.malwarebytes.com/
2. Deauthorize all other devices https://psteamproxy.yuanyoumao.com/twofactor/manage
3. Change passwords from a clean computer
4. Generate new backup codes for your Mobile App https://psteamproxy.yuanyoumao.com/twofactor/manage
5. Revoke the API key https://psteamcommunity.yuanyoumao.com/dev/apikey (there should be nothing in the APIKEY)

Also read here https://psteamhelp.yuanyoumao.com/en/faqs/view/3195-9FFB-BA06-F25B

its scam