Nick Reiner is calling BS on the executor of his trust ... telling the court he didn't give any consent to withhold money from him he says was owed to him under the terms of the trust when he turned 30.

Reiner filed a new legal document on Friday in which he says successor trustee Jodi Pais Montgomery's claim that he told a past trustee he'd leave the money in the account as "trust property" isn't true.

He also says the claim that his mother, Michele Reiner, told a previous trustee that he knew he could take the money when he turned 30 and therefore was consenting to leave it in the account when he didn't remove it is also not valid consent ... because he didn't authoritze his mother or anyone to make such a statement.

Reiner says he wasn't told by anyone he could take the money from the account, and he wants his money along with the accrued interest he's owed.  He says the trustee has listed these amounts owed at age 30 at around $558K.

As you know ... Reiner needs the cash for his legal defense. He was recently indicted for the murder of his parents, Rob and Michele.

He was briefly represented by attorney Alan Jackson ... who dropped his case when he couldn't pay his legal fees with the money in his trust.