The common expression “You’ve got another thing coming” is wrong.

If you think that’s the expression, then you have misheard the saying “You’ve got another think coming”

I was today years old when I learned the right phrase, and I couldn’t believe it myself. So, I googled it.

The expression mainly means, to rethink an idea or a thought.

Eg: “If you think you are going to get away with it, you’ve got another think coming”.

It basically means, think again.

So, If you think the expression is “you’ve got another thing coming, then you’ve got another think coming

Pun intended.