DFAS sent debt letter??

I was court martial’d in 2018 unfortunately due to being stupid. This was about July or so that year. I of course received pay up until the day of conviction when all pay stopped. After release I was sent home, they bought me a ticket and they shipped my belongings to where I currently live. FAST FORWARD 6-7 years, I get a letter stating that I owe over $14,000 for getting paid while on appellate leave and tuition assistance and SGLI or something of that sort neither of which is true, I havent received a single penny from them since the conviction so I dont understand how I would owe such an amount and I am pretty sure I could request bank statements that shows no such payments were ever made to me at all. Is this a common thing? I do not understand how an audit can even come up with such an amount. I am 100% sure I never received any pay from military since Ive been out.