Forerunner 920XT screen cracked after 3 days!!!

I purchased the Garmin Forerunner 920XT as it is meant to be a hardy triathlon watch. I had the watch for 3 days on which I took it on one cycle and one run. I noticed while wearing the watch that the screen had developed a small crack that ran from the center of the screen towards the edge. To my knowledge I do not recall hitting the watch against anything and there is no sign of impact on the watch. I returned the watch to the store which sent it off to Garmin repair center. Garmin now wants to charge me R2000 to repair the watch which I only had for 3 days and paid R8000 for. Surely there is a manufacturing flaw in the glass??? how can a watch built for triathlons be damaged so easily???? and surely this must be covered by the 7 day warranty