Depending on your company's specific plan you may not be vested in the company match. Vesting is when the money becomes yours. You should be able to determine if you were vested by reviewing the Summary Plan Document.
You always will get back 100% of what you contributed plus a percentage of teh employer match based on your vesting schedule and years of service. At most you'd be 100% vested after 6 years. Best to call the plan provider or plan advisor and ask.