Poor service at sunvalley dunlop express

Had a puncture (nail in tyre) repaired and tyre balanced at dunlop express sunvalley. Two days later on first drive tyre started losing air. On changing tyre discovered significant damage to side wall on inside of tyre at the equidistant places. Tyre was ruined and I suspect it was caused when tyre was removed from rim as no road hazard could conceivably have caused the regular spaced damage. Staff at dunlop express sunvalley vehemently denied any wrongdoing and refused to assist in any way.