Billpay Checks are actually Cashier's Checks and are drawn from account numbers that aren't your account, btw. It's one of the reasons it's far more secure to pay any bill requiring a check this way.

Check fraud is massively on the rise. They don't even need a physical check, just the info. They're printing their own checks now and depositing them electronically. They also hire homeless right off the street to go in and cash the checks for them. Homeless keeps $100, the fraudsters make the rest.

If you're using checks the way you say you are, it's only a matter of time before you have to deal with swapping out bank account numbers.