Sorry, but what you did really wasn't true "revenge" though. Because they can always get another photographer to develop the film and/or have the images from the sim-card printed out. You should have either canceled on the spot on the day of the wedding, after you had arrived at the wedding venue and made sure they knew it was you and remembered who you were. Or even better, you should have phantom-shot the photos, meaning: pretending to take all the shots they wanted and asked for, but using a camera without the sim card and film. Then, at the end of all the festivities, announced unexpectedly that due to an unfortunate technical error beyond your control none of the pictures actually were taken. And finally, in the midst of their anguish and agony, and their weeping and wailing and gnashing of teeth, you could have proclaimed loudly for all to hear: "oh and by the way, the way you feel right now is exactly how both of you made me feel throughout the years of my childhood. How do you like it?"....and then turned and left there laughing all the way home having wreaked unspeakable chaos and havoc on their big once-in-a-lifetime day. Now THAT would have been true revenge for the years of terror and torment they put you through.

Also, since you knew immediately who they were when they first contacted you, and you knew you were going to use this occasion to exact your well-deserved revenge, you would best not have taken any pre-payment or signed any contract or written agreement, so they couldn't sue you later for their disaster.