Experience letter for probationary employee who resigned. Is it mandatory?

We had an employee named X. He was on a probationary period of 6 months. He resigned after 5th month and said that he enjoyed his tenure with us and thanked us for the support. But due to his ill health caused by travelling to work, he is unable to perform his duties. Since he was a decent employee at the time he was granted leaves to recover and report to work to serve his notice. He then dropped an email a few days later with a list of demands saying if he were to stay back, he would want changes in his salary so that he can give time to the company on weekends (due to our nature of work), take additional responsibilities. He put a clause for himself that he would stick with the company for a year as part of the new list of demands. We agreed to the list and the increment in salary on the conditions of his tenure. And in a few days, he resigned again. This time he served 1 month notice out of the two and bought back one month. Thus we paid him his salary in full as per the new agreement in salary. However, due to such unprofessional behaviour and that he had resigned before completion of the notice period, we decided not wanting to give him an experience letter. Now that he is aware of this, he claims that we have inhumane working practices. That we have been mentally harassing him and the reason many people quit us is this. He claims that he resigned the first time also because his ill-health is due to mental stress. And that we forced his friends and family to post reviews. He then started threatening us saying you don't know who I am. Just google me. I will hire a lawyer and send you to court. We don't want to give an experience letter as he hasn't completed probation. Mid probation he resigned and is expecting an experience letter. He decided to sign up with us for the next one year based on the conditions he set for himself. Now he calls all of them inhumane. What do we do?