I am trying to get a hold of MANTECH. Does anyone know a way I can call their HR?

Maj Charles Miles is a Director at ManTech.

We also have 100+ RallyPoint members who work there... even if not in HR, I'm sure some of them are in a position to get you to the right person. As a personal tip, I think it's also always helpful to speak directly with the hiring/project manager, at least in addition to HR.

https://www.rallypoint.com/organizations/mantech-fairfax-va/current

Leigh Ann Capozzoli
Principal Technical Recruiter
Herndon, Virginia
Information Technology and Services
Email is [login to see]
Profile is
https://www.linkedin.com/in/lacapozz

http://www.mantech.com/about/Pages/Contact-Us.aspx

If we're talking about the same ManTech, here's the general contact page. The Employment Verification line can "usually" be used to get an HR department phone number, depending on what you are looking for.