Why would they send a letter with both addresses on it? That’s ridiculous. High street banks seem to be robots when it comes to things like this “we need him to prove who you are”, “i cant”, “well sorry”.
I’d like to think Monzo and even other fintech banks would be a lot more compassionate when dealing with this kind of situation.
What should happen is, you can dispute a joint account and then once you have both confirmed your identity you either mutually agree on who gets what from the account or the bank just splits it 50:50. I know 50:50 isn’t fair if more than 50% was technically yours but it would have been better than that guy spending tens of thousands while she was trying to gain access. or they could give you back everything that’s been sent from your personal account.