My previous employer had taxes taken out for my state. But they did not give the correct withholding number on my w2. I tried to contact them, but they won't respond.

Since you did not receive a w2, you file Form 4852 as a substitute w2.

The form 4852 is a last resort. This is what the form says:

 If you don’t receive the missing or corrected form from your employer or payer by the end of February, you may call the IRS at 800-829-1040 for assistance. You must provide your name, address (including ZIP code), phone number, social security number, and dates of employment. You must also provide your employer’s or payer’s name, address (including ZIP code), and phone number. The IRS will contact your employer or payer and request the missing form.

Because of this, you cannot e-file a return with a 4852, it must be mailed in.