The term for that is "interrobang." Wikipedia states,
The interrobang, also known as the interabang, (pron.: /ɪnˈtɛrəbæŋ/), ‽ (often represented by ?! or !?), is a nonstandard punctuation mark used in various written languages and intended to combine the functions of the question mark (also called the “interrogative point”) and the exclamation mark or exclamation point (known in printers’ and programmers' jargon as the “bang”). The glyph is a superimposition of these two marks.
It is a nonstandard (informal English) punctuation mark, that is used at the end of a sentence to express "excitement or disbelief in a form of a question, or asks a rhetorical question." As what Barrie England said, there is no rule for this type of mark—they are interchangeable, when the symbol "?!" is used other than "‽".
You should avoid this in formal writing. Visit this site to know more: WhiteSmoke.com. Points to ponder on:
Even in literary or dialog writing, over-use of the exclamation point should be avoided, using alternative wording or other punctuation marks to express emotion. Experienced writers know how to make their readers infer emotions from context.
Avoid: The Japanese food at Kyoto was just out of this world!!! Super-duper!!! These guys know how to cook!
[Exaggerated enthusiasm using too many exclamation points]
Consider: The Japanese food at Kyoto was the best we have ever had. It appears that the chefs there are highly professional. [Subtle enthusiasm using alternative wording with periods instead of exclamation points]
Do not use the exclamation point to express overt amazement or sarcasm. Use other words for rephrasing.
At 3.3 meters and 7 tons (!), the African elephant is the biggest (!) land animal on Earth. Yet, Johnny (!) thinks that the Indian elephant is bigger.
[1st exclamation point expresses amazement, 2nd exclamation point expresses sarcasm]
At a majestic 3.3 meters and 7 tons, the African elephant is the largest land animal on Earth. Yet, Johnny, stubbornly, thinks that the Indian elephant is larger.
[majestic expresses amazement, stubbornly expresses sarcasm, both instead of the exclamation point]