And there was no other major event that happened? We don't know if this is home insurance or auto insurance or health insurance or even something like marine vessel insurance. You didn't file a claim at all? Didn't get in an accident? Purchased a new/second home or vehicle? Changed jobs? Are you part of a program like DriveWise that monitors your driving habits? Had a recent medical procedure done? I think it awfully pre-mature to just assume that getting and cancelling a credit card would be the cause of this change.

EDIT: Heck, if 8% is a $400 increase, where do you live? Have you been affected by any recent natural disaster events? Have you added anything or changed your coverage at all?