What should I do about 401(k) theft?

My 401(K) is in one of the most conservative funds (mostly money market and bonds) offered by my company's plan provider (name: B**H, web: b**s.com). In the last few months, however, my account has lost about a quarter of its value. Moreover, postal mails and e-mails from the 401(K) provider have been missing in the same time period. Some of my personal info in the quarterly reports are obviously incorrect. I've tried to get answers from them for weeks. I think my account has been compromised--probably a case of identity theft. Instead of working with me to rule out identity theft, they work against me and give me the runaround. Should I report them to the authorities such as the FTC and SEC?