DFAS Retirement Pay and Failed Direct Deposits

Ok, back in February of this year, my uncle tried to change his direct deposit and mailing address with mypay, but, for whatever reason, it didn’t get changed. His retiree payment got sent back in February and it’s just now getting deposited to his new account for the month of June. He just got his statement via mypay, and it’s only showing his June money and not for the last 3 months that he’s been trying to get it straightened out. He’s a stubborn man, 83 years old… but my hero so I’m trying to find out how or if he will even get the pay from the last 3 months he didn’t get it. I do have POA for all his financial, medical and real estate issues. I know that social security doesn’t recognize that and we had to go to his doctor and do a bunch of stuff inorder to get them to even give me the time of day. I’m not sure what to do or where to start. Thanks.