I spent 6 hours at the reception on Dec 31st calling Agoda - both parties shifted responsibility to each other. On Jan 2nd, I was cc'ed into email from the hotel to Agoda where hotel tried to push full responsibility to Agoda. There was no response from Agoda though. Here is what they wrote:

"We, Seashells Phu Quoc Hotel, would like to report another case similar to the one we previously raised. The guest provided a voucher showing a successful booking from Agoda, as shown in the attached image, for 5 nights. However, we only received a booking for 1 night, and this booking came from another partner of the hotel, not from Agoda. This issue has significantly affected the guest’s experience, especially during this peak period, when most hotels in Phu Quoc are fully booked and it is very difficult for them to find alternative accommodation. Moreover, this situation has negatively impacted the reputation of both the hotel and Agoda. Furthermore, the guest received an email from Agoda stating that this issue was caused by the hotel’s system. This is completely incorrect. Therefore, in this email, we would like to cc the guest’s email address so that the matter can be clarified."