But, standing on principle, I would have really liked to lodge a complaint with the regulator. Only problem: Since I was acting as a company (that now no longer even existed), it was never a consumer transaction, so consumer complaint wasn't a viable route, and you obviously hurt your case, even if it's just a complaint with a regulator, if you then settle the balance since they'd read that as you admitting guilt in some way.

Not settling the balance and lodging a complaint with the regulator could have had the side-effect of raising the stakes for them. So in a situation where they'd not normally take you to court, they might now actually do that since there would now be real money at stake, if the regulator launches into a full-scale audit into their processes & business practices. In such a case, winning a court case against me would have helped them in calling off the dogs if the regulator were to take an interest.

If you ask me, it should be the other way round: The banking regulator should play the role of public prosecution. When you complain against them with the regulator, then the regulator should either (a) tell you to bugger off without charging you for the privilege and allow it to end right there (b) take on your case in the sense of taking it to court on their own dime and if it looks like it was processes & business practices that were at fault then they should come after the financial institution for that kind of a failure hard.