Liquid Damage on Waterproof Phone

Good day<br> <br> We are very unsatisfied with sony, they promise people a shatterproof glass and a waterproof phone.<br> When we book the phones in (M4 Aqua & Z3) it comes back as Beyond Economical Repair- Liquid damaged.<br> <br> Please help us because our client are getting mad at us about this but it is not our fault!<br> <br> Thank you