Show Cause notice from IT Company

Hi,

I joined an IT company and left the company after working for 4 days for a better opportunity.Before leaving the company I have mailed them my resignation mail and left the comapny and did not contact them again and did not respond to them if they tried to contact me.Now I got a show cause letter from the company saying that I was on unauthorized leave from some time and did not respond to their calls.If not replied in 48 hrs to the letter the legal action will be initiated.

I was in the company for 4 days,finished the joining formalities(signed the joining documents and took the appointment letter) but did not recieved the ID card.There was probation period for 3 months.The notice period was for 60 days but its not clear that it is applicable during the probation period or after completing the probation period.

Now I want to know,

What will be the legal action against me???

How strong/eligible would be the company to send me the show cause letter and take the legal actions on me in these circumstances??

What will happen if I dont reply to the show cause letter??

what should be my best next step of action??

Please advice me on this situation.Its a bit urgent for me.

Thanks in advance.

Thanks,
Chandra