I've first hand experience of this - they are a complete disgrace - don't waste endless energy on them, as they'll waste a hell of a lot of your time, trying to put obstacles in your path to stop you closing your account.
. .. Ongoing fees are only one of the obstacles, they'll also use excuses like needing to meet, having to fill out special forms, wanting further ID documents (despite having been provided correct ID documents previously), the sun not being in the right part of the sky when you wanted to close your account etc. etc.
Withdraw all of your money,
Give them written instructions to close your account (keep a copy), and expect them to refuse to act on it.
Make a formal complaint with them, for not acting on your instruction to close your account.
If they don't uphold your complaint, then make a complaint to the Ombudsman about them, you won't be the first to have gone that route!
Interestingly enough, you'll see them close the account and write off all charges that they applied after you instructed the account closure, before you get a final decision from the Ombudsman's office.
As I say, they are a complete disgrace - how they get away with this carry on, given the level of consumer protection that's supposed to exist, is simply beyond me.
The one question that I continue to struggle with, is whether their actions are strategic, or are out of pure incompetence.