I am feeling horrible, terrified and angry

[zfei]

my husband has 4 kids with the ex-wife. We have none. The ex-wife has re-married and has twins which are almost 3 years old with the current husband.
Everything has been ok, not great, but ok. Sometimes she could be a bit difficult but I always let my husband deal with her. He paid CSA every month, on time and didnt reduce any money when he was made redundant and has a lower pay job now. We get to see the kids every weekend and usually packed with activities. The 3rd boy is in taekwando class on saturday morning and the youngest in swimming lesson on sunday. We went to museums, parks etc. We have movie night every saturday. I am not greatest stepmum but I am happy with where I am.
The 3rd boy just got his grading and he is a blue belt now. He is then moved to the advanced class which start at 10.30 in the morning. Before this it was 9.30am and when we picked up the kids, it is usually the youngest boy want to tag along to see the class. The eldest two prefer to stay at the ex and we picked them up after the class finish.
Last night my husband texted the ex asking to pick them all up at 10.00am. Then she started to accuse my husband don't want to spend time with the kids. And the kids are missing him. My husband was annoyed not knowing where does this come from so he texted her back asking what she meant and is she mental saying things like that. So he said he will pick them all up at 9.00am as she was planning to take the twins out at 9.00am.
We showed up at 9.00am and her husband came to the door. My husband greeted and he just told my husband he is full of bullshit and he wants to talk to him about texting the wife for last minute changes about the kids' arrangement. She knows that the boy is going to be moved to advance class weeks ago, and my husband just asking does she want us to pick them all up at the same time which is 10.00am. I knew this is coming so i stood between the two guy. Telling him we just want to get the kids and we dont want to talk to him. Just trying to protect my husband as this guy has no right to say thing like that. He started to swear and keep shouting at me to shut up and saying i am rude and not being polite. I shouted towards the house for the kids saying we should go. He shut the door and shouting at my husband. My husband said this is between the wife and him so he doesnt have to hear him saying anything. He said something about the 4 kids are his and he could have them back.
I was terrified and angry. We started to walk away and I told him we are walking away and he should too. He followed us and still swearing at us.
Eventually we picked up the kids at 10.00am. The ex-wife said we walked away without picking up the kids and they were already getting ready at 9.00am. She also told my husband i shouldnt be shouting at her husband or verbally abused the husband.
I felt so shaken up and angry and started to feel sick.
I am not sure have i done this so wrong and i feel like why is this happening.

[quoteunquote]

Not a nice situation to happen over miscommunication,

I expect she was reacting to being called mental.

I would start with apologising for that, and saying that you would both like to get back on a civilised level.