What to do when you disagree with UI designer?

I have a little question, I am a full UX Designer, I don't do UI in my company. However, I have a regular problem when I am making user interviews then wireframes. The UI designers of my company said "No we can't do that because this journey is too complicated for us, so, it will obviously be too complicated for our users."

They don't want to create anything after that and they don't want to talk about it. What do you do in this situation? Do you testing your wireframes with the users to try and find support since the user interview findings doesn't provide enough weight of evidence?

Thanks