Is it identity theft if I claimed my child on my taxes?

I pay my child support monthly like I am supposed to. I work offshore 28/14 when I have my 14 days off I go get my daughter. I also buy school supplies, I take her to doctors when I am home, I go to her school when I am home because she has failed 2 times in 2 years. Her mother does not work at all! I claimed my daughter on my taxes this year, and I let her mother know that I was claiming her because her mother did not work. She responded through a text that saying that as long as I give her something. Which was fine because I already was going to give her something. I got 1000.00 tax credit for my child, I sent her mother 400.00 through child support once I received it. She sent me an email angry because I sent the money through child support, and told me that I can no longer get my daughter or call her. On the cell phone that I pay for so that my daughter can call me. She sent me a picture of an identity affidavit that she will be sending to the IRS. How is it identity theft, when she knew I was claiming my daughter? How is it identity theft when that is my child that I took care of financially all last year? And she didn't work all last year so why as her father I couldn't claim my own child? I can't afford an attorney right now. So I am trying to see if there is any steps that I can take on my own, to secure my visitation rights and when I should or should not claim my daughter on my taxes? Please help!