We cannot give you legal advice or know what court order you have to deal with (no lawyers here). But, in general, if there is a court order, that the ex gets to claim the child, it's inferred that you have to provide form 8332 and the child's SS#.
That said, and as the other reply already said, the IRS does not enforce court orders. It goes by it's own rules. If you claim the kid, the IRS will give you all the benefits. The ex's only remedy is to take you back to court. Being found in contempt is a possible outcome.
For more detail, see a similar question, asked by an ex, at https://ttlc.intuit.com/questions/3479726-my-ex-claimed-our-child-but-our-court-order-says-i-m-suppo...
