Why stockbroker gives funds back to my Bank Account even when not requested?

How ProStocks does Quarterly Settlement of funds of clients?

Funds (ledger balance in excess of margin requirement) of the client lying with stockbroker are required to be returned to the client at least once in every calendar quarter and there should not be a gap of more than 90 days between two such settlement dates for each client. This is SEBI mandated settlement and needs to be followed by each stockbroker in India.

The quarterly settlement of funds is subject to the following:

1. Balance in Trading Account (ledger balance in excess of margin requirement) in excess of Rs 10,000 on the quarterly settlement date, is called free balance and the entire free balance will be sent to your bank account.
2. In case the balance is less than Rs 10,000 in Trading Account then quarterly settlement is not required and the funds can be kept in the Trading Account till you want to withdraw or use towards trading and or investment, provided you had done trading in the current quarter. Otherwise, the full balance will be returned to your Bank Account mapped with ProStocks.
3. Those clients who have an open position in Futures and Options segment, a ledger balance in excess of 2.25 times of margin requirement is called free balance and the entire free balance will be credited back to your bank account.

Reference
https://www.nseindia.com/trade/members-faqs-actual-settlement-of-funds-and-securities