Ex refuses to sign Quit Claim on house. They released all interest in home three years ago in divorce?

Ex refuses to sign Quit Claim on house. They released all interest in home three years ago in divorce?
Added (1). Our divorced was finalized three years ago. He signed off on all interest in the home. I am not attempting to refinance and he states, he now wants 50% of the equity in the home. When we divorced it was 150K under water… But now that I was able to keep house and make payments and market has rebounded some what, he feels that he somehow deserves 50% of equity. I have made every payment for last FOUR years, one year prior to divorce and three after.
Added (2). Sorry, I am attempting to refinance. I am now at 20 years left and want to refinance to a 30… As I am one income and the last four have been a struggle, but I was able to hang onto house. No interest in selling, just want to refinance and have his name off house and off mortgage as he agreed to in the divorce.

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