Guarantee not worth the paper it is printed on!

I bought my parents watches at the end of August last year for their anniversary - these were gift-wrapped by the store and the Guarantee cards included in the box. In December we went on a family vacation overseas when my dad's watch stopped working. When we returned in January, he asked me to assist because he knew I bought it from a 'reputable' store. I went to Galaxy in Gateway in the first week of February with the watch and slip - they said perhaps it was the battery, I could shop and return in 20min, they would take it for a replacement. I returned and they then said that upon opening it appeared water damaged. The watch is clearly marked - water resistant 30m. My dad does not even swim- he is an elderly person! There is no reason for it to be water damaged! We asked for the manager-he/she was not there. We received an sms that we would be called - nobody calls! We call back, leave messages but nothing happens!