1. i prepaid estimated taxes and filed extension under married filing separately. so there was no return filed by me while making that estimated payment.=====> you made estimated pmt to IRS then of course you can get the refund from the IRS aslongas you owe NO tax to IRS.I mean you can not receive a tax refund if you owe for a prior year's / present year?s federal taxes . the IRS will automatically apply against taxes you owe.i guess you may try to get some help from taxpayer advocate svc. https://taxpayeradvocate.irs.gov/contact-us
2. My ex doesnt live in this country anymore and i dont have access to tax documents he filed.======>>Unless you filed your return as MFJ with your ex, your ex?s return filed as MFS is useless; no any info on your income or etc.
Please help, what should i do. do i still need to file 105c?======>105C is not filed by you, a taxpayer but by the IRS; the IRS uses a 105C form to inform you they are denying a claim that you filed for Refund.