Here's the truth: If you respond to a provocation from your ex, you will be starting your no contact from scratch. All over again. Yes, no contact can work a second, and even a third time, but it will require even more time and...why would you need that, anyway?
The best decision is to take a strong position and ignore all their attempts to provoke you, showing them that you've moved on and are not accessible. They would need to perform some hard work for you to notice them. This is how you reverse the power balance in your favor - if you want to get your ex back.
Now, if you've managed to ignore their attempts to provoke you, they will likely to suppress their ambitions and message you or call you AND it will still be a provocation. We call this 'a ping' message, and the whole purpose of ping messages is...you guessed this right, to test your availability. When you receive a message from your ex with a classic 'how are you', or get a call from your ex, you have two choices: