It is proper to withhold a get if you want to continue to be married to your wife.
However, if you want to get divorced, it is a mitzvah to give the get. Period.
And if a beit din orders you to give a get, it is a mitzvah to comply with that beit din. Period.
Money and child custody are separate issues. If your spouse (or ex-spouse) is acting improperly, she will have to answer in olam ha-ba.