Can my employer keep me from returning to work while on intermittent FMLA?

I've been on intermittent FMLA since January 2016. Each and every time I submit an intent to return to work or an email requesting that I want to work, HR states they have no work for me, or some other excuse. Yesterday's response was that I couldn't return to work until my FMLA is used up which is January 2017. At first, HR wouldn't even communicate with me. I'm not on short term, nor have been fired or laid off. I've not abused FMLA. I've nearly begged for work. I don't understand how this company can keep me from working if I'm an employee. I've had great employee reviews, and the government customers continue to ask me to return. Here is the last response from HR.
"Lockheed Martin is in receipt of several recent communications from you inquiring about your work status. The information received from you suggests your need for your current approved leave, which is intermittent Family and Medical Leave (FML) through January 28, 2017 for 2 episodes per week with each episode lasting 1 day, may have changed. If your need for FML has changed, please contact Sedgwick for further direction.
As previously communicated to you, there is no work for you to perform on the non-FML days during your approved FML. Lockheed Martin cannot provide an update regarding your work status until you have exhausted all approved FML."
I don't understand!!!