Payment of salary as well as ESIC during leave of absence on medical grounds- is this valid

I had to take leave of absence from office to undergo treatment after I met with an accident.
During said leave, I received full salary from my company and certain amount from ESIC towards my treatment. I had submitted the appropriate forms for ESIC and EPFO.
Now, ESIC is asking for me to return the amount given to me- I do not want to do this.
Kindly advice.