Notch job on an injector

[Guest]

I took my car to a mechanic took fit a new clutch and timing chains in my Hyundai ix35 6 months ago. The wife never drives on motors ways but I borrowed the car the other day and found it does not go above 3000 revs before losing power. We took it to a garage who said whoever fit the timing chains have drilled and siliconed a new, bigger bolt into the injector and it is now leaking fuel everywhere. We paid £1800 for the timing chain and clutch and when we told the mechanic our findings he said it was already like that but didn’t leak and he didn’t touch it. The garage disagree and say he must have to get to the timing chain. What can I do?