Dear Drshu,
The problems of this kind arise because the HR professionals in general and top leadership, in particular, do not understand the difference between the removal of the employees on account of "administrative reasons" and on "disciplinary grounds".
Under-performance is not an evil act as such. Yes, your previous employer had certain expectations from your position and since you could not meet those expectations, they have removed you. Removal from the job is nothing but a punishment. Therefore, explain to your employer that for whatever has happened in the previous company, you have been punished already. If the current employer also takes action for what has happened in the previous employment it will be double punishment and it is against the Indian jurisprudence. Principles of natural justice enshrined in the constitution do not allow more than one punishment even for the crime also.
Address your letter to the MD of the company. However, route it through the HR department.
General Comments: - The post shows the psyche of Indians in general. People always expect everyone to succeed every time and failure is considered morally bad or wrong. It is considered that those who fail once, will fail forever. This is nothing but social bias. The sooner the HR professionals get rid of it, better for the society.
Thanks,
Dinesh Divekar