Problem with 2 employees

Dear Sir, We are a coaching institute based in Gurgaon. We pay every teacher's salary on 20th of the following month. For ex, Sept salary will be paid by 20th of Oct. This is how we pay them since over 6 months. Unfortunately, June's and July's salary got delayed by around 7 days. For ex, June's salary was cleared by 25th of July instead of 20th of July. Now we have a situation. Two employees threatened us that unless Aug salary is not paid by 5th of sept, they wont take the classes. And in the middle of the syllabus they paused they paused the classes. This was un acceptable as student's careers were at stake and we couldn't resolve to their threat. Therefore, we told them that no payment will be made if they make this threat. As a result we blocked their aug salaries. And terminated them. Till now we haven't given them Experience certificate. All the communicated has been over whatsapp and email and therefore is documented, Now what is happening is they are defaming me and my institute bluntly on social media. And also threatening to do many things. How should I respond?