Sony Z3 repair

So I booked my Sony Mobile Sony Z3 in for repairs at MTN Westgate , because the earphone jack stopped working and the speakers on the phone were crackling. Everything else was perfect. Phone is otherwise in perfect condition. The consultant at the store checked the liquid damage indicator and wrote down that this indicator shows no liquid damage. I checked up on the phone now and they told me the phone is beyond economical repair because of liquid damage. *** MTN. Funny thing, the phone is marketed and sold as being Water proof under certain conditions. Now they just assume those conditions were not met and automatically just void the warranty. How's that for customer service. The customer is always wrong in this instance. Can I please get somebody to look into this from MTN and not just assume. These devices aren't cheap to replace anymore, that's why I opted to go for a dust and waterproof phone. Even had a 5 layer screen protector on with a shock proof casing on from Cellucity. I looked after it. The phone is still at your repair center, MTN, and I must pay a fee now to get my \beyond economical repair"phone back"