That doesn’t sound quite right but the answer that they gave would of course depend on what exactly it was that you asked. If you asked whether you can keep the prepaid card for example, I’d understand that answer.
It’s also worth mentioning that as far as I know, Monzo have not yet designed any features for people with mental health conditions. Instead that’s something that they plan to do. In the meantime, it’s great to hear that you found a way to use the standard functionality to address your needs so let’s see whether there’s another way to do that now.
There’s a couple of ways that may work, that I can think of.
The most simple option could be to not make your current account your primary bank account (the one that you store all of your money in) & to give your wife control over topping up your Monzo account, by bank transfer or card.
The other option might be to use Pots to set aside all of your money in your Monzo current account apart from £x, that you can spend each day.
I’m less sure that using Pots will enable you to lock the rest of your money away - you might still be able to ‘break into’ another Pot but we’re waiting for more details about the feature - so option 1 seems like the most likely solution to me.
Might that work for you?