The wife's lawyer is wrong. If the property settlement agreement says it is to be shared, ex is in violation. That's a legal issue.
It could have been direct deposited 1/2 to each of 2 accounts.
If it was a check, it required both signatures to cash. Did ex forge a signature? That's a legal issue, too.
The attorney would file the papers with the courts to have the spouse that kept the money held in contempt if the agreement was to split it.
You filed the return, whatever happens with that refund afterwards is none of your concern.