Balance belt broke???

I took my Pajero to a shop specializing in these engines and had my crank shaft pulley replaced. They had taken off the belts including the balancing belt and put them all back on. 2 weeks later the balancing belt broke and went into the timing belt causing it to jump. There is now damage to the engine and I'm not sure if the shop is to blame or is it just coincidence. Please let me know your thoughts, Thanks