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."
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
ˌit’s/ˌthat’s not ˈmy problem(spoken, informal) used to show that you do not care about somebody else’s difficulties: Well, I’m sorry you feel that way, but I’m afraid it’s not my problem.
Farlex Partner Idioms Dictionary © Farlex 2017