Tire Sidewall problems of the 1999 Volkswagen Beetle

When tires were rotated, the technician found three bulges on the inside sidewall of the left rear tire. The goodyear dealer claimed it was road damage and would not honor the tire warranty. The tire was less than two years old and had gone less than 20,000 miles. It had replaced the original, whose sidewall was punctured when my wife hit something in the road. I suspect that the sidewalls on this model tire should be stronger than they are.