Dealing with government agencies is always horrible. Whether it be the DMV, SSDI, Child Support, IRS, whatever. A terribly managed slow moving machine that makes a lot of mistakes and is slow to correct them when you point them out.
I have no advice for you, because all of my attempts to deal with agencies in the past have been as aggravating as yours. I can only say my thoughts are with you as you go through the motions to set things straight. It's always a long process with many long phone calls that go nowhere.
Well I guess the only advice for you is if you have the means physically go to the office. They are a little more responsive when you're in their face. I hear you about the poorly placed offices though, usually in sketch parts of town and are hard to get to. Annoying.
Good luck