Your message is clear and polite, but you can make it sound a little more natural and firm. Here is a smoother version you can use:
Hello Support Team,
My Steam account is currently linked to an EA account that is not mine and uses an email address I do not recognize. I do not have access to that EA account and believe it was linked by mistake.
I would really appreciate your help in unlinking my Steam account from this incorrect EA account so I can connect it to my own EA account. Please let me know what verification information you need from me to proceed with this request.
Thank you for your time and assistance.
Kind regards,
Rajib Saha