Loss of power (sluggish) and unexpextedly stalling whilst driving

My car had been misfiring (rough idle and a bit underpowered) and also smelt badly of fuel when started. The engine light came on so I took it to the mechanic to have it repaired. They replaced the brake pads and rotors. They also replaced the timing belt (which they informed me was 12000kms overdue) so that they could diagnose the cause of the problems. They said something about cylinder 2 misfiring and replaced the coil pack. They had a bit of trouble getting the engine light off which I thought was strange. I needed my car back (as they'd already had it for longer than expected) so they said I was fine to come get it as everything was fixed, it was just the light. Half an hour later I got there and they said they fixed the engine light issue on their last test run.
When I drove it home I noticed the car felt extremely sluggish/heavy. It's usually a zippy little car so I just thought if it still feels like this in a few days I'd call them.
Then next day I started my car and it felt like a truck. It still felt sluggish and wasn't idling well. As I was driving along the car just shut off - every dash light came on, had no power steering and obviously no engine power at all - I rolled to the side of the road and turned the key off. I waited 10 seconds then started the car and cautiously kept driving. When I'd pull up at the lights the cars revs would go up and down repeatedly (down to almost no revs, then quickly up to 2/2000rpm). On my way home it stalled once whilst I was slowing down to a set of lights, and felt like it was on the verge of dying all the time.

So it's back at the mechanics and I was hoping someone could give me a little info on what might be going on as I feel like I'm being screwed here. When I took it back they said it looked like cylinder 1 was misfiring now. I've already spent $2100 in total with them over the past 3 weeks (had a major service before timing belt etc was done) and it's very frustrating.