We dont know if it’s snapped or come off we only have the original RAC report which doesn’t say
OK so If I am understanding the situation is as follows.
Your son goes to this garage pays £1300 for a 2005 Punto Mk2B XBOX edition
essentially paid cash as it was a bank transfer rather than via finance or credit card.
This is a 1.2 16 valve so it has what's called an "interference engine" meaning if the cambelt snaps the valves and pistons occupy the same space and collide causing the engine damage. (just for reference the 8valve engines do not do this, if the belt snaps you pop a new one on and keep driving)
The car fails the day after purchase.
So The RAC came out had a look and said "the car has a failed cam belt with a previously failed cam belt tensioner " I am going to ignore the plugs.
You presumably went to the garage said the car has a broken cambelt and they said "tough luck sold as seen, haven't even looked at it.
Now £1300 for that car is top price, and well over the odds for the mileage
I want you to go to Parkers.co.uk and print off this
https://www.parkers.co.uk/fiat/punto/hatchback-2003/12-16v-xbox-3d/78/free-valuation/
Click on the ( i ) beside the dealers price and it will give you an idea of what you can expect. It may be worth paying a fiver for a custom valuation.
This will give some weight to the fact that the car was clearly not "sold as seen" i.e they where selling it at top price from a dealership so should expect to have the same service as any other car they sell.
The MOT history shows that it was living in Liverpool in January, Clearly had a pretty Poor MOT and was not retested so presumably the owner scrapped it or sold it off cheap, maybe traded it in with a dealership or someone like webuyanycar. It probably went to auction and ended up with this dealer, who must have done some work to be able to sell it, and there must be some record of that.
The fact they sold it with 3months later with an MOT suggests that they did not intend it to be "sold as seen" They put effort into preparing the car for sale as a roadworthy car, which goes back to that expectation as a customer that the car be "fit for purpose"
Without knowing what the RAC actually did when they inspected it, its hard to comment if the cambelt is actually broken, how they establised it had previously had a cam belt tensioner failure etc.
What you need is to know for sure what has actually.
Did the car break down or did it just not start?
Knowing what the fault is will instruct what you do next as it may only be worth scrap. It may be worth repairing.
Knowing the fault yourself will mean you can either say you have lost the full value of the car all £1300 or if it needs repair and it will cost £500 for repair, then you may only be entitled to claim £500 against the company.
Rather than going in all guns blazing at this point I would be paying a visit to the dealership with all the paperwork you have, on a nice busy weekend day and having a loud conversation about the car you bought breaking down the next day and what are they going to do about it. Make it "Available" to them. "It is not drivable but it is Parked at ...... here is the key for you to go and collect it."
If they are still refusing you will have to look at getting it repaired yourself or if it cannot be repaired, it may have to be scrapped, and you'll need to keep records and sue for what ever your out of pocket expenses are. (i'd be including a couple of pints of fuel for the price of paying them a visit at the dealership to get it resolved)
Once you have a known value of loss, records to say what went wrong, the cost of repair or receipt showing what you paid. you can take this all to court and no judge would rule against you.
Just bare in mind that this company has only existed since 02/07/2020 with the previous company MCH Motors ltd being dissolved on the 25/01/2020. (same director) it may be they are the sort of people who will suddenly disappear if you do end up in court, (change the company name again and dissolve the old one) however if the money was paid into the account of a private individual then you may be able to sue them instead of the company.
The Google rating for this Business is pretty high so I don't think one review from a one of customer will make much difference, would just look like one disgruntled customer out of the 88 positive reviews they do have.