Hey, took my bike for a service as the brakes and hub needed replacing. The bike shop said they didn't have the hub in stock so I would have to wait to have that done but they could do the brakes and give it a service also they recommended changing the chain and the rear cassette.
Picked it up this morning, got 100m down the road, put it into top gear on the front and the chain slip and wrap around the front derailleur. Shin went down the front cogs and then went over the top. Now have 12 stitches and other injuries.

What is my stance when I go back to the shop? I took the bike straight back and said look after it while I go to hospital the wound is deep. They did a quick inspeciton and said they suspect it slipped because the front cogs are worn. Before I went to the shop I had no slipping or bad gear changing, they just based the need to change on the measuring tool. I was given no advice on the front cogs.

Any advice appreciated, thanks