I had joined a college in ist round of neet ug counselling. and then left that seat 3 months had passed but the college hasn't refund the fee yet how much time is given by mci to college to refund the fee

If you have joined and then quit the college, it is unlikely that you will get a refund. Refund is for those candidates who paid the security deposit but haven't been allotted any seat even after all the rounds of Counselling. But if it is a free exit is what you chose, then you should be eligible for a refund. MCC has released the refunds for the eligible Candidates already. The list has been updated on their official website at: https://mcc.nic.in/ . Right now, the site is under maintenance but yes, the refunds have been processed.