Military Severance Pay Verification

I got medically separated this past May. Before the separation I was told o would be receiving severance pay as well. I was told it would be in the mid 60’s range. About a month after I was separated I got the check and it was only 19k. So there is issue number 1, trying to figure that out. The biggest issue we’re facing now is that we are in the process of buying a house and the bank is seeing the large deposit into the account and is wanting proof of where it came from. Bank statements don’t work, I called my bank and had them write an official letter stating where that payment originated from and the transaction details but that won’t work either. I’ve called the VA and they’ve told me they don’t deal with it and to call DFAS. I called them and they told me they don’t deal with it, to contact my unit admin who in turn stated they have nothing to do with it and can’t access anything regarding it. Do any of yall know who I can call and get not only the verification of pay/proof of where it came from but also figure out why my payment was so low?