Can I have right to give negative reviews on social page

I actually do not know my problem belong to which law...my name is sandhya and i took skin peeling session from Rejové clinic which is located in green park,Delhi. It was very bad experience for me and I shared this experience on their Facebook page than Dr. Priyanka (rejove clinic) called me and offered me dental services on behalf of that which I don’t wanted so I told her to return my money so she said we can’t refund u can take any other service worth rs 2500 thn I agreed on that after few days she again changed her line and said I can give u only dental service. We were talking about that and thn from her side I got this message ..., Dear Sandhya Chaudhary , We presume either 1) you are a history cheater , and you have targeted many service medical companies in the past 2) you are abusive and give threats 3) you are trying to defame us in purpose to extort money out of the company , completely convinced you are doing all this on purpose . In any case we have decide to file a case of defermation , we have enough proofs , you will have to pay for the damage caused on purpose , the defermation amount will be according to company evaluation in present market (between 1crore to 5 crores) Consider this a final notice , before going the legal way. Now what can I do they r giving me mental torcher