On becoming sick, you took leave. But then were you in touch with the approving authority about your sickness? How did you communicate with the authorities? You have sent mail through HR portal but was it approved first?
Though it is not explained in your post, I feel that you have been issued memo because of the non-communication with the approving authority. The second reason could be lack of trust. The authorities to whom you report, might have perceived that your sickness was fictitious!
Anyway, give a reply mentioning your sickness. Let your reply be in chronological order. Attach medical certificate (not doctor's prescription) to your reply.
From India, Bangalore
From India, Mumbai
The disciplinary authority,
In response to the memo no. dated , this to reply as follows:
1. I was really unwell on ../../.. and hence took one day C.L. which has been sanctioned. I resumed duty and was in office on ../../.., ../../.. & ../../..
2. But as my condition deteriorated and needed urgent medical attention, I took medical advise and was advised three days rest. (Is he company recognised doctor). A copy of the medical certificate is attached. I had informed HR Dept by mail attaching copy of medical certificate. A
copy of the mail is attached to this reply.
3. After the period of rest I resumed duty on ../../.. but was shocked to receive the memo accusing me of having failed to discharge of duty with devotion , diligence and care.
It is submitted the above sequence of events show that the absence was on genuine grounds and does not in any way show failure to discharge duty with devotion , diligence and care. These are serious accusations on my character and an isolated instance cannot lead to such a conclusion. I have been honest and hard working, committed to complete the assignments given and honour the commitments made by me.
In the above facts and circumstances, it is submitted that the honourable authority may note satisfaction over the reply and close the proceedings.
From India, Mumbai
In your case, you were sick and presume that medical documents to prove your case.Make a simple reply attach copies of your medical treatment and fitness to rejoin duty.
I am sure you would have given a fitness certificate from doctor when you joined duty.
From India, Pune