PayPal sends IPN(Instant Payment Notification) messages even after you have cancelled your Chargebee account. To stop receiving IPNs you will have to manually turn off the IPNs under My Account >> Profile >> My Selling Tools >> Click Update corresponding to Instant Payment Notifications >> Turn Off IPN . Given below is an image for your reference.

Even after you've turned off IPN, there are chances that you receive IPN emails. These are likely subsequent attempts of IPNs that were triggered before you've changed the setting since the IPNs that failed are resent for 4 days.