Often a series of simple questions are needed to resolve an issue for a customer. It can then be simply to much to fill in a form and communicate through email or inefficient to communicate through the phone. Thats why I propose an online chat that could have multiple functions like giving intelligent answers to questions that might require counter questions or simply give you some guidance.
Another idea would be to also have a function where you watch a real time screencast (video) in your browser where the web service person can visually show you how to navigate the site. I think these ideas are important for sites that are as complex as the tax agency web site and compliments each other.