BM unwilling to have child call dad

I’m nervous to post because I had posted a different question to the r/Parenting and the responses were so cruel and mean. I had to delete the post because I couldn’t believe the conclusions people were jumping to based off of the blurb I had posted. But, maybe it’s because they didn’t have the context of being a stepparent or maybe I ran into a bunch of trolls.

But here goes to trying again because I’ve seen how supportive this community can be.

Context: my husband has a ten year old with his ex. It gets complicated because they are first cousins and the reason why they had a relationship and a child is because when she was 17 and he was 13, she began grooming him. She used a fake religious text to convince him that they were the reborn Adam and Eve. She convinced him to run away and get married, have a baby, etc. They separated when he finally realized how their whole history was a farce and the religion wasn’t real. At the time of separation, she gained full custody because he was scared she would hurt their son if he refused. After much back and forth over the years, he regained 50/50 custody. Not even a year after, she filed for relocation and it was granted.

We’ve been coping with all the changes, but the question I was hoping for productive advice and suggestions is my husband has phone privileges with his son daily and he has his own little iPod that we can directly call. But, my husband has had trouble reaching him. His son has shared that his mom makes it uncomfortable for him to call. She’ll say things like, “you’re calling again? You talked to your dad yesterday.” Last night, my husband reached a breaking point because it had been three days since they had talked. He texted his ex and asked for their son to call. She responded with, “I’m watching a movie.”

My husband has tried mediation, but she has refused to go. We’ve tried going to court but it’s become very expensive, especially after the relocation trial and she’s made it a point to say that we are combative since we keep resorting to the courts. But, she either ignores or refuses to follow the parenting agreement and I’m not sure what else we can do. My husband has tried reaching out to her mother (his aunt) and her brother (his cousin) for help and they both became very angry and said that he has failed to step up as a father and they cannot be involved with this.

Has anyone had experience with a high conflict, but also refusing to yield, coparent? What do you suggest we do? My husband just wants to be able to check in each day, no more than a 5-10 min chat.