i was once last year sent a notice to pay a quarterly PAYG. i knew i had paid this and had the receipt to prove it, but wondered what would happen. paid the initial payment by CC, paid the overdue notice by CC. about 4 weeks later received a cheque in the mail for the extra payment. but did hold my baited breath as i didn't want them to re=credit the CC for obvious reasons, but yes, it was a cheque in the mail.