What I would do (might not work, I don't know your group) would be, no raising corpses, just trap THE FUCK out of dungeon. First guy that comes in (if the DM's a bro, he probably won't just have you starve to death), gets killed by the traps (could be something simple like setting rocks up to fall at certain points) - or you could just kill the poor schmuck yourself, but he might have friends with him, so I recommend traps.
Now that you can leave, what you want to do is study as much necromancy as you can, but don't use any of it. Learn all you can about it in secret, but play up how you were treated unjustly and locked away for no reason. Try to gain followers any way you can - money (if there's a big crypt in the dungeon, you can probably sell some shit), or if you're charismatic, you could probably attract a few followers just because you were 'treated so unjustly'.
Make your home in the dungeon - not because it can be easily defended, but because that is where you were put as punishment. It was unjust, but who are you to question a man of god? Leave in secret, if at all.
Try to get word out to your former party. Try to get a face to face with the Paladin. You just want him to see that you were innocent, that you still are innocent, and that he treated you unfairly. Sure, maybe through some righteous indignation in there - if you're being completely 'forgive and forget', he might get suspicious.
Once he agrees to a face to face (he's a Paladin, should be easy to manipulate), set up a room for it, prepare the room for a fight. Once he's in the room, you kill him - use any knowledge you have, your necromancy, whatever.
Now, preferably, you're locked away in a room in a dungeon filled with long dead corpses, some people who might like you, and your former party. The corpse of the paladin is in the room with you. You raise him first (it's a matter of principle), then you raise the rest of the corpses in the dungeon.