How to account for a supplier refund when no actual credit note received

SOLVED

If we have received a refund on a) a cancelled event and b) an invoice mistakenly issued to the company but have received no actual credit note (nor will we), do I need to post a credit note anyway otherwise I will not have anything to allocate my refund to. And how would I date this credit note? We are not VAT registered so no VAT implications. Thank you very much