Yes. Using the ‘Call moderator’ option from inside the game is better than the ‘Report’ option because it automatically provides a link to the game in question for the mod.
If you are feeling patient then await a mod. If you can’t wait or don’t feel inclined to wait, then resign or allow their victory and trust the mods to deal with it later. Note, the best they can do is annull the game but repeat offenders will obviously be dealt with.
[Edit] See also: FAQ