What if I changed my paypal account on a cash receiving day?

If you changed your PayPal email address, you should just receive a notification at the old address telling you that someone has sent you a payment. You can add up to 8 email addresses to your PayPal account, so you just need to put it back on your PayPal account to accept the payment. If you got a notification at your new address, it should have already been credited to your account. If it wasn't, check the email again. It might have been an e-Check that requires time to clear before the funds appear in your account. It also could be that you received a fake notification, and a payment wasn't really sent. Check the headers of the email and see what email address it was really sent from to be sure.