Sandone Tire supposedly fixed my exhaust problem, car back fired before I left the lot, was told -it's ok scranton, Pennsylvania

I took my vehicle in for exhaust repair of the front of the car. I was leaking water. They stopped the water leak, telling me I had a hole in the exhaust line and that they fixed it. They said they replaced a timing belt and water pump too.  I no sooner backed out of the lot and the car backfires. I complained and  said that the car was awfully loud also and was told it was ok.  That trip cost me over $500. Since then, I could still smell some exhaust in the car and the car continued to sound awfully loud.  Six months later, I went to firestone for an inspection and was told I needed the whole exhaust and muffler replaced.  They fixed it costing me another $700.  It now runs smooth and quiet. So what did sandone tire fix??  or not?? They had just replaced the exhaust a year earlier!