>>5773616[The Dark Gods are not in the business of benevolence for its own sake, and are known for their spite. An offered favour to your mother isn't an oath to do whatever you want whenever you want, even when you're actively undermining and disobeying them. Again, not really looking to litigate the decisions, but a more in-depth explanation is below.]
If you wanted to get highly technical and litigious about it with the one and only proper god in the pantheon who even cares about keeping promises, he'd say he already did you plenty of solids and offered you lots of opportunities nobody else gets (being allowed to live and being treated as a 'real' Dragonborn all your life, being given direct audience with the Dark Gods and having the chance to be an Antipaladin, being offered guidance and divine intervention, etc), and whatever 'debt' was there has been paid with interest. Meanwhile your refusal of orders and violations of the Knight Ascendant oaths, your swearing of oaths to place other obligations ABOVE the Dark Gods (to humans and paladins, no less!), your unilateral modification of the religious doctrines in your kingdom, and your determination to strike out on your own and achieve power by heretical means rather than by making amends and regaining Divine Favour are all pretty non-kosher. The Dark Gods probably feel that not smiting or otherwise acting against you would constitute a pretty big favour after all that. You can disagree if you'd like, but if your contention is that they aren't being 'fair'... They ARE the DARK Gods for a reason. If you wanted truly benevolent, altruistic deities who seem to genuinely care about fair play with their mortals, those are the other guys, and your culture considers them silly weaklings for it. 