Knocking noise.

I have a 2005 Nissan altima and I have had hell
with this car. It made a loud rattling / knocking
noise when driving and gets louder when I hit the
gas and settles down a bit when I release the gas.  
I broke down on a 20 min drive and it overheated
and made a horrible sound of rattling very loud.
And it shut off on me randomly and became very
hard to turn. And wouldn't turn on for about 30
minutes.  When it did come on it made that noice
again.loudly.
I took it to a machanic and he said it was a rod.
And needed a engine. So he said he'd put a used
working engine in it . 600 for the engine. Then 600
for the labor. So months later I get it back. 3 days I
drive it and take it on a 30 min drive on the highway
and it starts to loose acceleration,  the noise
comes back and it starts to smoke and I pull over. I
got it towed back to the machanic  because I didn't
want to risk anything.
He told me it was a cylinoid making that sound and
it was nothing hardly.
And he said he would fix the cylinoid and change
the oil for me.
Month later. (Yeah. This guy take too long)
He says it's done and good to go.
And that his wife "drove it" for about 40 min.
So it's "good".
I get in it. And take off.
I didn't hear a noise for a bit.
Then 15 min later on the long road to my house
(took the long way to check the car out). The
sound came ... the same damn sound that had
been happening.  I head my way home asap.  The
sound would get louder as i hit the gas.And down
the road before the hill. It shuts off on me.
Becoming hard to steer and starts smoking. The
gage showed no sign of overheating. ( i think it's
broke) but got it towed up to my house from sone
old guy asking me for money first ,( which i said i
had no money. ) he says good luck then leaves.
then I guess feeling bad for me  he turned around
and hooked me up and towed me to my house.
After 30 min the car started. And it had the noise
and me and my uncle checked the oil and it had
metal shavings and what seemed like grease in it.
And now I'm unsure what to do.
Is it just trash now? Think my Machanic ripped me
off? Any input would be helpful. Thanks