Could I have done anything differently?

[sg622]

Brief backstory is ex and I have 2 kids together, DS6 and DD4. We've both moved on and usually co-parent pretty well. DS6 is quite a sensitive child and has struggled with our separation. He hero worships his dad and lives for EOW and every Wednesday when he goes to stay with him.

Ex now has a new partner, let's call her Ann, who has a 7 year old daughter, let's call her Bella. Ann and Bella moved in with ex in January and DS6 has found this a very difficult change. He misses being able to spend time with just his dad and DD. He used to have a room at his dad's house where he chose the wallpaper and bedding and kept some of his own toys, but this has now been redecorated and converted to Bella's room. DS now sleeps in with his sister in her unicorn themed room (a horror for any 6 year old boy!) and doesn't have his own space at his dad's house any more. I totally understand why this is because it is a 3 bed house and Bella lives there full time, but I think it could have been handled with a bit more sensitivity and consideration as to how it would look to DS. I raised with my ex how upset DS had been and suggested that he should maybe try to spend a bit of 1-1 time with him to reassure him. Ex seemed to agree but nothing ever happened.

Recently DS has seemed really down and a bit reluctant to go to his dad's - the total opposite of how he is usually. He has eventually told me that Bella is being mean to him when he is there - not sharing her toys, calling him names and telling him that ex is her dad now and loves her more than him. I'm not sure how much is her being deliberately horrible and how much is him being overly sensitive, but either way he is upset and it needs to be addressed, so I gave ex a call last week to chat about it.

Ann is now absolutely livid with me, saying I am accusing her child of being a bully, trying to turn ex and the kids against her, I am manipulative, interfering, it is my fault that DS is so sensitive, he is liar and spoilt brat. At the weekend when I dropped the kids off she wouldn't speak to me and her manner with them was really harsh. ExH has totally taken her side communications this week have been absolutely awful. I am absolutely dreading having to take the kids round tomorrow, and am so worried Ann will take her issues with me out on the kids. My question is, is there anything I could have done to handle this better or anything I can do now to try and resolve things? I'm aware co-parenting isn't easy and there are bound to be issues adjusting to a new family set up, but this has just blown up so spectacularly that I think I have just made things worse for all of us.