First, relax.
Second, keep a record of everything including who you talk to and when.
Third, stop calling DFAS. MAke finance do their J-O-B. Go ask to speak to a supervisor and sit and talk with them about this until a CMS case is opened.
Fourth, if you can't get finance to do their job then speak with your supervisor, first shirt and/or commander. They will get some action.
Keep records and emails so that when you ultimately file and if you owe you can write a letter an ask the IRS to forego any penalties and/or interest since this really wasn't your fault. Go ahead and file on time if you don't get a corrected W-2. If you get a W-2C afterwards, then file an amended return and write the letter. It is amazing what that will do.