Did your house keeper go in and take photos @Jeanna28
A guest looking for other accommodation on their laptop/phone doesn't stop your housekeeper from checking the property
confirm your housekeeper turned up within twenty minutes of their complaint about 2 ants and some breadcrumbs and they refused her access to do a walkthrough /address any issues so there was no opportunity to check on/adress their concerns
just say you're sorry that they decided not to stay and if they cancel any refund will be processed under the cancellation policy they booked under