Defamation

I have been working with a company for the past 5 months, the company is a call center which works as a lead generator for different companies in australia. Recently they asked me to resign based on performance issue. Key Points to be noted. 1. I was hired as a Quality analyst for the company in the month of May. 2. I was asked to be on calls to generate leads which i had done for a week/10 days after which i was given my role that i was hired for. 3. In July the company asked me to be on calls once again to support the staff which I agreed for. 4. In August, since one of the processes of the company was suffering in lead generation, I volunteered to be on calls for the month and see if i could be able to do something. unfortunately it did not work in my favour. During this period, however, the company removed me from my designation as QA and assigned me the role of a normal agent (BDC) and set parameters like KPI on me. They also paid me as per BDC payout. 5. In September I am put under review stating that my performance was not good and that I would need to work on the same. The same month I gave them 14 leads, which as per the previous months was better. 6. In October they asked me to leave stating that my performance is not good and that they were expecting me to hit atleast 20 leads. 7. After they asked me to leave, I mentioned that I would delete all my leads from the system, however the system does not allow one to delete all leads at once. It has to be done, one by one, and since I had only 10 mins at hand, the same was not possible. Instead I assigned the leads to my team leader. 8. Now the company states that they are unable to locate the leads and have blocked my salary as well as advertised on social media against hiring me by another other company, without prior intimation or acknowledgement. My Questions: 1. What is the procedure to be followed by the company, in terms of blocking salary as well as advertising in social media of not employing a person based on reason of misconduct?. 2. Should the employee be made aware by his former employer that the company is going to advertise on social media that he should not be employed by any other company? 3. If this not the right practise, can a case for defamation be put against the company in question?. Please do advise on the same.