to be going to vs future/present continuous

Hello,
Both of the sentences sound fine to me, but do you consider them different?
"Tell mum that I am not going to have dinner tonight, "Tell mum that I won't be having dinner tonight"

Also, what do you think about "Tell mum that I am not having dinner tonight" and "Tell mum that I won't have dinner tonight"? I've heard people say that. I don't think I would use them, but I assume they are okay. Are they?

I am sorry, but I couldn't put "future simple" in the text box.