The answer to this interesting question lies in the name of the nonstandard punctuation mark “interrobang.”
This is what an interrobang looks like:
The fact that it’s a question mark + exclamation mark suggests that “?!” is correct. (The question mark comes before the exclamation point in the name.)
The interrobang is used in an emphatic rhetorical question, as seen in the following examples:
Keep in mind that the interrobang (and “?!”) are considered nonstandard. Do not use them in formal writing, e.g., school essays or business letters.