Re: my cupcakes gone completely wrong 
You didn’t add baking powder?? If yes, then this is the main reason your cake came out flat,crispy!! I don’t think there’s a cake recipe in which baking powder isn’t used!!! It’s the main ingredient so never skip it.
Btw, sorry I said beat eggs and sugar together(Somehow I thought it was a cheesecake)..in this case beat butter and sugar first!