How do I change the support order, to cancel or fight the state for arrears, when I have proof of me having the kids over 50%?

For the past 6 years I have been ordered to pay $1000 dollars a month, with 50/50 custody. The past 3 years living in AZ work has died and I have had state assistance, for me and the children. My ex wife makes 3 times the amount of money than I have ever made, expecially at the time that the support order was set. I have proof that I have the kids for more than 80% of the year and a letter from my ex wife stating that she does not want child support any more due to my financial instability, I have had that letter for 6 months. Every year I have filed with the court for a change or support order due to my financial state, and the fact that I have the children more than the divorce decree states, The change order basically states that my ex-wife should have been paying me at least 600 per month. But not one time did the court call for a hearing, and I am now over 24,000 in arrears, with proof of no work. I am affraid of going to jail for 1, and I have the oppertunity to go to Texas and work offshore, but I don't want them to take all of the money I need to get caught back up after all these years of no work. So I'm asking if there is a way to stop the arrears prove that I should not have to pay them, and actually change the support order? And another question is how do I get full custody of my kids, when I know that my children do not want to be with their mother, She has pore health, and only seems to care for herself, During a stint of sickness, she called me and begged me to come and take the kids because she was to sick to handle them, that same night after I picked up the kids, she was arrested for a DUI, she does not cook or at least very rarily, she feeds them only fast food, Another example is my youngest broke her elbow under the time my exwife was resposible, I came to the doctor to check on her, the doctor gave us both directions of what to do for the care of her. My ex wife then took my daughter back home and I expected that everything would be fine, I called on the day that she was supposed to take my daughter in for a cast, she said she had an appointment, 2 weeks later when I picked up my kids for my time with them my daughter still had the splint on from the E.R. So I freaked out and took her to another doctor that stated it was to late, and now her arm has healed crooked due to my ex not following through with the doctors orders, I know my ex is selfish, goes on vacations all the time for weeks not ever taking the kids, she has to work out of town 8 days a month, to where if I am not there to watch them she takes them to anyone who will take them for her. I can go on and on and I have 5 years of calanders that have been filled out for everyday that I have the kids, and everytime my ex has threatened me, I now have to move to Texas for work, I want full custody, and hope fully, justicfully want to fix my arrears, and or my child support situation, My ex just threatens me about sending me to prison for arrears, and that there is no way I could ever get full custody , Is this true and what can I do? - Is this your question? Add additional information