Welcome @8675309 to the forum, sorry to hear that the HO has cancelled your sit without the courtesy of informing you about it or explaining the reason.
You are correct a sit should not be cancelled by either HO or sitter unless there is an unavoidable and extraordinary circumstances. It’s also impolite not to have also sent you a message about the cancellation.
Contact member services.
Support@trustedhousesitters.com
With regards to the HO still has a live listing for the same dates, I think that is what happens automatically when a sitter is unconfirmed. The HO may not realise that the dates are still live.
Definitely contact member services.