Rejecting Bonanza's contention that the violations were technical or venial in nature, the watchdog said the delay in resolving the complaints within the stipulated time was not "inadvertent".
A fine of Rs 20 lakh has been imposed on the company for violating stock broker regulations.
The entity was already warned on one occasion for not having a prudent investor grievance handling mechanism pursuant to inspection, Sebi said in an order.
"The noticee (Bonanza Portfolio) had taken more than 30 days to reply/act upon 54 out of 281 complaints i.E. 19 per cent of the complaints received were replied/ acted upon only after 30 days.
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Bonanza Portfolio could not be reached immediately for comments.
Sebi had carried out an inspection during a period of FY 2012-13 and FY 2013-14 till the date of inspection -- June 19, 2013. It looked at the books of accounts and other records of Bonanza Portfolio to examine whether adequate steps for redressal of investor grievance were being taken by it, among others.
Being a stock broker with a vast clientele, Bonanza failed to fulfill its duty of complying with the brokers regulation during the inspection period, the order said.
"It is of utmost importance that every stock broker assigns high priority to investor grievances and takes all necessary steps to redress the grievances of investors at the earliest, which the noticee failed to do at the relevant point in time," it noted.
The penalty has to be paid within 45 days of receiving the order.