well, check to see if it's manufactured for the same region as your Wii. since the wii is not region free, and you got the game from out of country this would be the first thing on the trouble shooting check list.
if not, you're going to have to replace it with one that is for your region. Unless of course you've got your wii hacked/modded to be region free. If the game is the correct region then you've more than likely got a defective disc. This happened to me when I purchased Mortal Kombat vs. DCU for the 360, i had to exchange it about 3 times before I got a working disc, still don't know why since all the other games worked and the discs weren't scratched nor was the system dirty. Electronics are finicky that way.
In regards to how you can get a guarantee/refund/return or whatever, my suggestion would be at the very least see if you can track down some sort of support number or customer support for the company/store that you purchased it from.
If you can't remember the name of the store, or its too far to return to, you just may be out of luck.