Please Help Chev Aveo is going to be the death of me

Hi Everyone,

Our Chev Aveo is going to be the death of me, im hopeing you could help me out.

Our Chev went in to have the head replaced, we blew it pushing the car a bit too hard on a highway in Johannesburg South Africa last year this time. The car stood for a while, we were looking for someone who could help do the car at our home because we couldnt tow the car. So a guy came arund, used ot work for VW and seemed legit. He took everythign apart, took our money and ditched. Didnt fix a thing. We then tried to do a few things ourselves, we changed pistons, bought new ones. Still no luck so finally we got the car to a reputable company and they fixed every thing up. Sadly, even once we had gotten the car back there was a failry high pitched whine when we revved the car. But she was going and we were happy about that.

From then things have gone down hills. The next lot of problems in order to happen are these:

1. loss of power in any gear range, worse on lower ranges however
2. whine got worse
3. Spit type sound comes from exhaust when changing gears

Most recent now to start, started yesterday, is a knocking sound from the right hand side of the car (drivers side in South Africa), and a rubbing type noise from the left side of the car (passenger side in SA). I put herup and tried to take a look but no real luck. Just started her up to try and see whats going on and it is seriously down on power and has just misfired out of the airbox.

The engine light has been on constantly since we got it back from the mech. He has tried to read codes, no success. He has tried to clear the codes and it goes off for a bit and comes right back on.

Any any advice will be so much appreciated!
Thanks, Dom