Still getting notices after P45 filed?

I got a notice today from HMRC to tick the 'student loan' box for a client's (ex)employee. Oops i thought... I mustn't have filed their P45(for leavers) yet... yet when I checked on quickbooks which I use for payroll it says that the P45 was filed on 28th April. Any ideas why HMRC are sending notices for an employee who's no longer employed? Is it just a glitch in the system or does it mean that HMRC haven't received the P45?
Privacy Policy