Lack of communication is one of the most difficult things to deal with as a stage manager and, unfortunately, there is only so much you can do to fix it. You can only work with the tools you're given. From what you've described, it sounds like this company does not have much experience with working with a stage manager and you may be a victim to "this is the way we've always done it." I've found that a lot of smaller companies, particularly ones that haven't had a stage manager, sometimes have a lot of difficulties adjusting to having one. They frequently don't understand what that work relationship entails. It can be as simple as someone not realizing that the thing they've always been responsible for in the past now belongs under the stage manager's umbrella. Making one person responsible for a lot of tasks that were divided among a large number of people takes more work than people realize. They may think that they are hiring a miracle worker who will make everything better, not realizing that they will also have to work on the relationship.
It may be worth having a sit down discussion with this artistic director about everything that has happened and the difficulties you had. The important thing in that kind of meeting is to not sound like you are trying to shift blame but that you are trying to understand where the breakdown in communication happened and what the company as a whole can do to make things better for everyone. Did you have regular meetings? Are there notes from those meetings? Were regular reports sent out? Those are things you can refer back to. If they are unwilling to meet with you, then it is probably time to cut your losses. Either the company is not ready for a true stage manager or it is not a good fit for you. Either way, it's time to move on.
In the future, when you interview for a position or when you are first on board it is best to ask a lot of questions. Who is responsible for that? When are the production meetings? What are my expected duties? Be very clear in your own communications. When in doubt, document everything. If you are not getting what you need to do your job, then make the higher ups aware of it.
Example:
Dear artistic director,
I have attempted to contact "so-and-so" regarding "situation" but have not received a response. Do you know an alternative way of contacting them? Any assistance on this matter would be appreciated.
Sincerely,
etc etc
Dear prop person,
It came to my attention today that a baby doll prop has been added to the show. Could we meet briefly today to go over the prop list to make sure that everything I have is up to date?
Thanks,
etc etc
At the end of the day, all you can do is your best.