Engaging With The Powerful

I live in a small city by international standards - about 1.5 million residents. But we have our fair share of bureaucracy... at the moment I'm dealing with a breach of contract and I'm in two minds...
In New Zealand we have a "Consumer Guarantees Act" (of Parliament). I'm on the right side of the law, they are not.
Do I stand my ground or give in and walk away from a fight?