This is so simple to prevent, it's just a matter of prompting. The fact that the bank didn't proactively secure against this makes me glad that I'm not one of their customers.
I am not OP, but completely isolating the AI from any actions other than what's expected would be a start. IE a specific API only for the AI, in which there is not even any access for the prompt injection to even make sense. But just an idea from an onlooker.