When you called, who did you talk to at the hotel? Whenever situation like this arise, you need to ensure your talking to someone with the power to make the necessary change.

Each hotel might operate a little differently. But, where I worked, you would have had to speak to a Supervisor or Manager in either Reservations or the Front Desk. If those people aren't available, you could try the Manager-on-Duty or Night Manager. If you weren't talking to one of those people, you can try calling back. When you call, say something like: I need to speak to Manager at the hotel (not Central Reservations) about an issue with a reservation for arrival tomorrow.

For best results, offer to change your stay to a different weekend instead of just canceling. (That assumes you will do that. Don't lie.)

That said, the hotel is certainly within their rights to say no. We expect hotels to honor the terms of the reservation. The reverse is true, too.