Alimony

Assuming that 1) you are in Belgium, 2) your ex is in Belgium and 3) you have a legal Belgian divorce agreement (i.e. a constat de divorce approved and agreed by the judge that specifically mentions alimoney payments due on your divorce), then the answer is probably yes.
If you got divorced here, you should speak to either your lawyer, or the notaire who drew up your constat de divorce.
If you didn't get divorced here, then it will be problematic and depend on where you got divorced, whether the Belgian courts recognize your divorce agreement, and if they are prepared to enforce it.