You shouldn't need evidence to show that you are single. If you were previously married and got divorced then you would need to provide a translated certified copy of the divorce but you don't need to prove to an immigration officer that you were never married.
I am afraid you are in a limbo. To be on the safe side, find an immigration attorney and have a consultation. I know FLorida has some Russian speaking attorneys, Besides, based on your post you may not even need that and can reach out to any attorney not necessarily Russian speaking.
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Nothing requires you to prove who the fathers of your children are in connection with your I130/I485 application if you were not married to them. If you were married to them, all that's required is proof of divorce. You may want to retain an immigration attorney to assist you with preparing and filing your documents. Good luck.
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