Ok first off i'm in the US and on ssi disability. When i worked i payed child support though there has never been any court order. I then had go on disability and lost contact with them(they were out of state). Then a couple years ago the mother contacted me out of the blue saying she had moved and that she had known how to contact me for a year. She acted nice and put the act on that wanted to get along. So i moved up there to help her out with bills and such(big mistake) she basically made life a living hell between lieing manipulation and all kinds of things. She taught the kids(one mine and one some drug dealer she hooked up with who was in prison) to lie and would threaten them if they listened to what i said basically making it impossible to have any kind of decent relation ship with my kid. So eventually I had to move back out and back to my home state. well once i got set up in new place and phone on I tryed calling to give them my info but phone was turned off( I had payed the phone and electric bill days before leaving) and from what I know she moved with me noway to contact them. So anyways fast forward to today and i receive in the mail a letter for back child support out of nowhere. Now there was no court ordered child support to begin with so I don't see how can be past due pay and I had no idea where they were to begin with to of sent any money anyways. I guess I want to know how this can be and what rights I have? It is not even a matter of not wanting to pay but that i'm on a very limited income and had no idea where they were to begin with and still don't really. Does anyone with some experience with this have some answers, everything online seems to be geared toward trying get money form someone?

Edit: while I was living up their I tried get her to do group counseling with me that she outright refused. She also at one point went and told me she only used me to have the kid and that it wasn't my responsibility (though i took responsibility anyways or least tried to though she made it near impossible to accomplish anything). Even when my child was born she said she didn't want child support and when at one point I brought up my kid living with me she threatened to run off and go into hiding with my kid. She is also very fake religious as in she only uses it to make herself look good and disregarded it when it doesn't suit her and even went so far as telling my kid I was a devil worshiper because i had something about Buddhism on a old myspace page I hadn't used in years. Unfortunately due to illness I do not handle stress well and obviously this is extremely stressful situation.