One: saying you can't use Weapons to defend against fangs/claws/fists is a clear houserule (and one I wouldn't want to play with.)
Two: If your gaming group insists on it (remember: FATE's rule zero isn't "The GM is right" - the other players should definitely get a say here), then it would be entirely fair for you to be allowed to retcon your character - perhaps removing the riposte stunt, perhaps even re-building to use Fists skill instead of Weapons. (I use "retcon" deliberately - this isn't an in character change, it's an out-of-character response to a rules change; if you do this, then whatever you end up with is, in character, how he's always been.)
Three: You also deserve an explanation of why your GM made that change. If, for example, it's because your character was totally dominating fight scenes and the other players weren't having fun, then you should work with your gaming group to fix that. If it's just that your character was effective enough that the GM wasn't having fun... well, you should still find a way to fix that, but him arbitrarily nerfing your character isn't the right way. Instead, you should look for ways to work with him; perhaps by finding self-compels like "Well, this showdown is in a museum - I doubt the mundane security will let me walk in with a sword..."