My Derailleur got destroyed

[albatross54]

I bought a specailized Hardrock MTB about a month ago I have been using it so far on Roads, paths and forests but nothing really heavy the chain started skipping so I took it back to the shop and "fixed it" a week later I was about 5 miles into a ride and starting to go up a steepish hill so changing down gears on the back gears having been in the lowest gear on the front. The chain snapped and the derailleur snapped and twisted in on itself so i now have scratches on the disk of the gears and basically was completely messed up I took it back again and they had no idea how it happened fixed it i had to pay for a new derailleur but wasnt much but i try to ride today and the chain which they "fixed" not replaced is skipping again what should i do ??

[Painkiller]

Complete drivetrain inspection is in order here. Make sure derailleur is aligned, inspect the rear cluster for damaged teeth or excessive wobble, inspect front chainring for the same. replace the chain. use a different shop if you have too.

[Bill]

Also check the spokes of the rear wheel in case the chain wrapped them a good one!