I am on a J-1 visa for 3 years. My employer has withheld my social security and medicare in error for the past two years. They are continuing to withhold in my third year. How can I get them to stop withholding? They have refused to give me back my money for the first two years and I have filed forms with the IRS. How can I be sure that I will get my money back as it was withheld in error?

J1 visa is exempt for residency for 2-years. It also depends upon tax treaty with your country and the purpose of visa. During 2 years you must file nonresident tax return

Normally for third year you must pay FICA taxes. You are also not exempt from residency and may have to file resident tax return.

For refund of FICA taxes you will file form 843. Read: Your U.S. Tax Return: Social Security and Medicare (FICA) Taxes for Non-resident Exempt Individual