I've looked further around the area in question, and from the direction you approached it (up from beneath) and that the builder used mossy cobble which occurs naturally in dungeons, I can infer that you didn't know it was owned prior to breaking into it and destroying the spawner.
After taking this into consideration, your clean ban history and giving you the benefit of the doubt, I'm approving your appeal. I'm removing the ban ASAP. Sorry for the misunderstanding.