Hey all, my first post but really need advice!

I have a Suzuki Jimny O2, mine is a 2003 model and still under
warranty.  There is exsessive vibration in the steering wheel when I
hit 50mph?  This has been happening for nearly 2 years and the garage
have said they cannot find what the problem is.  I find this very hard
to believe. They are now blaming me for the alloy wheels being
unbalanced, surely this is their fault? Any advice from anyone would
be great as this is really getting on my nerves.  The work they have
already done is:  replaced the brakes and discs 3 times, replaced the
cam belt due to an oil leak, replaced various other parts due to oil
leaks, surely this is going to be a problem in the future.  I have
heard that if your car has been for repair more than three times for
the same problem and they cannot fix it, then you can get a refund for
replacement.  Does anyone know the law on this?  I am really desperate
to get this sorted, please help!