Why can 言ってんじゃねーぞ be an order?

Question

I've been learning japanese for quite a while and always wondered why :

言ってんじゃねえぞ

could be an order. Whereas something like :

言わない

can't be an order.

Because basically, 【言ってんじゃねぞ】 is just :

言う　の　テ形

助動詞　いる not pronounced since it's a contraction

Contraction of the particle の (ん)

And じゃない

So I don't understand why 【○○てんじゃねえぞ】can be understood as :

"Don't ***"

Thanks

Answer 1

Expanding the contraction 言ってんじゃねぇぞ, you get 言っているのではないぞ as you say, which is a のだ form negated. Now, a のだ form can be used as a virtual order and its negative form can be prohibition.