I'm wondering whether i can use a colon in the following way:

(A judge says in the court) It has been ascertained that : A is a legally existing bank. B is a shipping company. A lent a loan to B. B paid the first two installments and defaulted on the remaining. A demanded B's immediate redress of their default. B did nothing in response. A froze B's bank account. A sued B before this court.

the above is a fabricated example. when i actually do the writing, there are much more complicated things to describe following the colon. so I guess you won't tell me to round up all these things in one sentence.

thank you all.
Hi anon,

I'm just a learner, but here are my two cents.

I don't normally see a colon after "it has been ascertained that".

Perhaps this helps:

Colons are a lot less attractive for several reasons: firstly, they give you the feeling of being rather ordered around, or at least having your nose pointed in a direction you might not be inclined to take if left to yourself, and, secondly, you suspect you’re in for one of those sentences that will be labeling the points to be made: firstly, secondly and so forth, with the implication that you haven’t sense enough to keep track of a sequence of notions without having them numbered.

Source: Notes on Punctuation by Lewis Thomas
This guy certainly doesn't like colons. haha.
Julielai's comments are always worth more than two cents.

What follows is really only two cents: (note my colon)

Uses of the Colon [from a longer list]

1. After an independent clause that precedes a list.

2. To separate an explanation, rule, or example from a preceding independent clause.

The problem with your clause ('It has been ascertained that') is probably that it ends in 'that'. Can you write, 'It has been ascertained:' or are you quoting the judge?