The damned DOS number can never be through, I do not know this siduation has been changed or not. And I do not know the tel number. You have to find by yourself. The INS number is 800-375-5283. The case status website is https://egov.immigration.gov/graphics/cris/jsps/index.jsp?textFlag=N. There is information about how to do when you have not got anything from INS after you obtain the letter from DOS. Good luck.