My husband has two kids from a previous relationship. They…

My husband has two kids from a previous relationship. They do not speak very much and dont have a good relationship. They were not married. He has been paying child support based on a court order from a province out west. Now he's been in Ontario for a few years, and he got paperwork recently saying the account is closed. He has contacted his ex, and she had gotten this paperwork a couple months before him, but didnt tell him. His money had been direct deposited into the old account.. He has gotten this money back however. He has contacted her several times, and tried to give her the child support payments into her account, but she will not even speak to him, and says she's filled out paper work to start up a new account in this Province, and that she wants everything to be legal. Im wondering if she can ask for back pay from him for being under a different province, even though he was just following his court order? I dont think he knew that the pay is different in all the Provinces..
Over the years, she has used her children against him, and basically got custody of the kids when he was not in a good situation.. She has no concern for his wellbeing, or that he now has a new family with a new baby. I'm concerned now because I dont want her to say he stopped paying support, hes been trying to do this, but she wont even speak with him, it's very frustrating for him. He didnt realize this, but I think Ontario has a higher rate of child support payments? This will destroy us, as we have bought a house and also have a new child, and I no longer have a job at the moment.. I just feel like he has no rights, he has also spent lots of extra money and time going to see his kids, bought them extra gifts, clothing, guitars, shoes, bikes, food, activities and more. Unfortunately he did not keep these reciepts... His kids are now 17 and 16 and I think the payments end at age 18? He will still help out his kids, but we just want to be out of her grasp, it's horrible how she has treated him over the years, and she is the one who actually cheated on him when he left her. He was jobless, because they worked together, and he could not bare to be at work, because she cheated on him with their coworkers, then she showed up at the childs babtism with one of the guys she cheated with , and he was holding my husbands baby.. It took everything my husband had to sit through the babtism under those circumstances. So, when he was literally homeless, sleeping in his friends office, she took him to court to get full custody of the kids at this time-how cruel of her. He ended up joining the military and now also suffers with PTSD from his tours.. There was one incident in the past when he came to visit his kids, took 2 weeks of work, drove to Ontario from Alberta, and she decided to take the kids on a trip for a week without telling him, knowing he was coming to see his kids-completely inconsiderate. So he then had to wait for them to get back and lost a whole week with them.. That is just one small example of how she has behaved. She basically collects her money every month, and does not help him in any way be close to the kids or encourage it. He has spent thousands in gas and hotels driving 3 hours one way to see them on weekends when we can..She has never once helped in that way... He's tried his best to be a good dad, but she has not made it easy for him. I was also wondering, my husband could have asked her to provide him with reciepts for how she spends the money? When she ends up with huge tattoos on her arm, and he has to buy his son pants and proper running shoes for school, it is a bit frustrating, when he alrady was giving her a monthly amount for his kids. I just have this bad feeling she is just going to try and get whatever she can out of him now because the kids are almost adults, and it worried me, because she wont even talk to him, or answer his calls. He feels like he has no rights, and it's causing alot of extra stress on him, which he really doesnt need. He is a good guy here and we need some advice. I just want us to be prepared. Is there anything we can do?? I hope you can help us with some infromation. Thanks, G