Keep in mind that there are human spammers as well who do research and work for bots. By supplying answers to 3/4 of these questions in the question itself, you're making their lives very easy. These questions, in general, are rather easy and your target niche don't need those answers in question. If these questions are old, it may be well that the bots/humans have discovered these answers.
You'll also want to switch to hCAPTCHA and ensure you have "Difficult" set for the passing method if you continue to get hit hard.
Be sure to also flag all these users as spammers as that will tell our Spam Defense of them.