I think you will probably find somewhere in the carriers' Conditions of carriage, that they can substitute their aircraft with that of another carriers if necessary. They fulfilled their end of the bargain (ha ha) so to speak by carrying you from BRU to LCA.
If you are dissatisfied with the service, then a letter of (reasonably strong) complaint maybe the only way to get something back if that is what you are after.
Otherwise, vote with your feet.