First off - an easy thing that you can do, that is an old belief, for breaking curses is to simply spit in the direction of the curse. Or to simply spit directly in front of you then walk over it (you do not need to step in it).
Secondly, the Threefold Law applies to Wiccans (or other pagans who choose to adhere to it). By telling someone that they've been punished by the Threefold Law without knowing their beliefs would be the same as having said "It was just God punishing you for being a sinner." It is very rude to assert your own beliefs on another.
Thirdly, Karma is a specific belief where the actions of this life - both good and bad ones, affect how your Next Life goes. Karma is tied in with the belief of reincarnation - you cannot have one without the other. Karma Does Not mean "what goes around comes around" like so many think it does.
Lastly, other basic ways to rid oneself of a curse can simply be a purification or cleansing bath. You can make one with salt, purification herbs (lists can be found in the herbalism forum), etc.
Good luck in your endeavors, OP!