Defect/poor quality crocs slip-ons

I have been purchasing crocs shoes for myself and family over the past 5/6 years. I have not had any defects or faults until a recent incident with my son's slip-on's. The white rubber/plastic covering by the heel of the shoe has detached and despite trying to glue it back on, keeps coming undone. I tried to get assistance at the Crocs store at Mall of Africa where despite being told that I would need a slip in order to have the shoes repaired or replaced, the assistant still escalated the matter to head office, as I hadn't retained the slip. Unfortunately head office refused to assist, despite the obvious evidence of a manufacturing default on the shoe, considering that this was a second pair I had bought of the same slip-on, only because my son had outgrown his first pair which was still intact at the time of purchase. I'm disappointed at this, as I had bought into the price for these shoes justifying their quality.