it's/that's not my problem
be not (one's) problem
To not be one's responsibility, duty, or concern; to not be something one cares about or intends to be involved with. I know you're worried about paying back your loan, but your financial issues are simply not my problem—you're the one who decided to get into debt. A: "But sir, there's no way we can satisfy the requirement if my husband isn't allowed to work here in the first place!" B: "That's not my problem, ma'am. Those are the rules."