"You've got another thing coming"
Thank you for reply in advance,
***** NOT A TEACHER *****
(1) I don't know how you used that phrase.
(2) But here is one possible explanation:
TOM: I'm in big trouble. I need $100 right now. Could you lend me a hundred bucks, please?
MONA: What? You expect ME to lend you a hundred dollars? Every day you treat me rudely. You never compliment me. You never thank me. And now that you're in trouble, you come to me for money. Listen here, my friend. YOU HAVE GOT ANOTHER THING COMING!!! = You are not going to get the 100 dollars from me. You are going to get ANOTHER (an + other = one other) thing. That "other thing" is NOTHING! Not one penny from me.
Thank you for your question.