Hey, so you can still file a chargeback as per Visa's rules.
Even though the transaction date may be outside of the 120 day time frame, your date of stay still has not passed.
You can use the date that HotelPower.com notified you that the reservation was canceled as a 'Date of Discovery' to put you back within Visa's timeframes to submit a chargeback.
I would contact your financial institution and have them help you file a Services Not Received claim.
They will likely require you to send a copy of the email/letter from HotelPower.com to substantiate the claim, but you should be good.
If you financial institution tells you that they can't file a chargeback, they're wrong. Visa's dispute rules can be found online via Visaonline.com