No, there's no agency you can report the bank to for their failure to give you a phone call back. If they called you back and said you're turned down, you still wouldn't have anyone to complain to.
It's really not surprising that the specialist isn't returning your calls, though, as these lenders are notoriously incompetent, and will wait until April 18th to tell you that you didn't submit all the right paperwork, don't make enough income, or couldn't qualify for the modification. They'll just put it off as long as possible.
So you might want to keep trying to get in contact with someone there (try other people in the same department and explain that you haven't had a phone call back in 45 days), but also try other options. There are professional companies that specialize in this kind of loss mitigation negotiation, and others that can help refinance, work with an investors, etc. You'll just have to figure out what the best ways to stop foreclosure are for your situation.
As a last resort, go to the courthouse and ask for a hearing before the judge. Explain that you've been trying to work out a modification outside of the legal process, and had been told you would receive an answer, and that you haven't gotten one. The judge can order the lender to give you your answer, or not allow them to go through with the foreclosure process. That means keeping the sale date off the schedule until the bank lets you know.
Going to the court like this may seem intimidating, but the clerks can usually tell you which form to fill out to request a hearing. Then make sure you bring records of your calls and documents, and explain that you're getting screwed.
Complaining to someone will get you a form letter saying the bank didn't do anything wrong, and the foreclosure will proceed. But using the courts can force the bank to get their act together, or else they'll have to pay their attorneys more, and have the foreclosure postponed.