Have you ever been in a situation where you're a cog in a big company your work depends on other people's action and you can't get them to do their part so that you can finish your own tasks?
If the answer is yes, you know how frustrating this can be. This happens because the other people involved have their own priorities and you're at the very bottom.
In order to get things done, you have to get to the top of their list and the solution is rather simple:
Create a carefully non-personal, non-emotional email in which you explain the situation, place the person responsibile in the "To:" field and add their direct manager, your own manager, and anyone remotely responsible in the "Cc" field.
I guarantee your problem will be solved in no time. :D
You can even escalate this further up the chain with a follow-up email where you add more managers up the chain in the "Cc:" field.
Don't forget to thank everyone involved after your issue is solved.