Leela, I'm sorry I didn't see your reply until now.
The phone number excuse as to why you weren't notified is obviously bogus.
As you were then speaking directly with your sister, she no longer had an excuse yet from your description, it appears she did not offer information on your father's condition but you had to ask. Further, while there is no reason to withhold, she refused to provide you with the location of the hospice where he is currently located. She/they obviously want to ensure you don't attend, whether you intended to or not. It is likely the only notice you would have received if any, is after he passed.
Since they no longer have an excuse of not knowing your phone number, perhaps it is more fitting for your mother to call you at her convenience, if she wishes to talk. The responsibility is then on her