You may have to call in a plumber to see what's blocking your toilet.
A plumbers tool called a snake.
Try squirting dish soap in it then flush. That should make it flush but you do need to find out what the problem is if it happens again.
Rent a snake and see if that does it for you.
Somewhere I read dump a can of coke in the toilet. Let it stand for a couple of hours then try flushing. I hope I am remembering this correctly.