A few years ago, I cancled a day 24hrs in advance and got a similar message from my agency.
I called Boots central resourcing and told them and they explained that wasn’t there policy, I’m probably wrong but I bet there is some kind of discrimination risk if you ‘blacklist’ someone. Low and behold I was working again.
Wouldn’t be surprised if it was the Agency getting there own back because you’ve caused them an issue. I dropped that agency, and never had a booking issue since.