Really need advice now, faulty car with warranty? [Merged]

I'm 20 and got my first car from JCT600 in August after passing my test in May. Thinking that JCT were a reputable company, I thought I'd be in safe hands. I wasn't.

I bought a late 2011 Vauxhall Corsa Limited Edition from them. When I got it, I was nervous about driving so I didn't really drive far, but about a week later, I started motorway driving and noticed the steering wheel was shaky, I just thought it was normal for 70mph.
Although I took a motorway lesson with my instructor in his car, he asked me if the wheel was shaky and that he needed to check his wheel nuts after so many miles as he'd just had some tires changed. I told him his wheel was stiff but normal, although my own car was shaky, he told me I'd just need a balancing and they're not all that expensive.

I took it into Kwik Fit a few days later for just the two front wheels balancing. The passenger side wheel balanced fine, but when the drivers side wheel was placed on the machine, it was bouncing. The mechanic told me the wheel was warped and needed a new alloy. He told me it had been caused by somebody curbing the car at high speed. I could guarantee that wasn't myself, I'd only had the car around 2/3 weeks and I was too worried to go at high speeds.

I took the car to JCT as I felt it should be their responsibility to replace it. They took it into their service centre, told me there was nothing wrong with the wheel, they just rebalanced it themselves. So I got the car home before I realised they'd totally replaced the alloy. I said no more about it though. I couldn't really be bothered with the hassle anymore.

So aside from the way they treat me over the wheel..
I started to notice when driving that the car wasn't really gaining much power. First gear was the worst, I'd have to over-rev for it to move and then the change to two would be very jerky. Second to third etc would be fine, it was mainly first to second, as well as a delay in first. I thought it might have just been me worrying or it was all in my head, but after so long I realised I wasn't imagining it, and I took it into a local mechanic last week. He checked the error codes and said there was nothing there and assumed it may be the timing chain that's stretched as it can be common with Corsas, but the repair for that would be about £400/£500.

He offered me a full service with oil and other filter changes and everything so I took it. Afterwards, he told me the car still had its original spark plugs in there and they were rusted solid inside, and confirmed the timing chain is stretched and it's up to me when I'd like it sorting out.

I spoke to my grandparents' neighbour after and he was asking me how my car was, I told him we're having nothing but trouble with it and mentioned the timing chain, he listened to my engine running and said it's definitely rattling (he's an independent car dealer as well as maintains them)

I decided again that this should be a JCT issue, at the end of the day they've given me a year's warranty, promised the car was serviced before I got it and it simply wasn't. Even on the phone when booking it in though, I got a mechanic saying "I don't think a timing chain will cause the car to be sluggish but we'll look.."

I don't know much about cars but I know if a timing chain isn't functioning properly, then neither do the valves and cylinders. My grandad complained to head office and they just told him their services just offer an oil change, but regardless, even that car hadn't had an oil change, the colour of it before my service last week was just solid black. I thought that was normal.

Anyway, I'm worried they're going to turn around and say there's nothing wrong with it, or lie about something or try and charge me. I just don't know any more, their customer service is shocking.

I'll also add that the car was around 29,000 miles when I got it and now it's at around 33,000

Any advice?