Quite popular excuse from Nokia Care. Many users reported that they lied about oxidized parts (suggesting, that phone was drowned). If You're 100% sure that they lie - which I'm almost sure also, judging on experiences from other users - I would go along every step of formal complain process, and if that doesn't not help, I would try lawsuit. Really.

In meantime, I would write about my experiences to some newspaper magazines, federal consumer law organizations (or any equivalent in Your country), mobile devices forums etc. Nokia "oxym.oron" care is behavior is just unacceptable.