Are brokerages required to step-up the cost basis of securities in an inherited account?

When my father passed (in 2018), he left a brokerage account with several securities. These securities were split between myself and my brother and are currently held in separate brokerage accounts at the same brokerage.

It’s my understanding that the cost basis of these securities should be adjusted to reflect the price at the time my father passed.

I requested that the broker make these adjustments for all of the securities several years ago, and yet the basis remains the same in both accounts as it was when my father died.

I again made the request in mid October of this year, and almost two months later, the cost basis of all securities remains the same, with no step-up/down of the basis.

My question is, is there some sort of law/rule that requires brokerages to make this adjustment when it is requested? I know that it was made a requirement for brokerages to report the cost basis of securities back in 2013, so I was wondering if there was any part of this law that requires them to step-up the cost basis when they transfer brokerage accounts from the decedent to the beneficiaries or at least when requested to do so?