HTC Desire Z :: Qwerty Back-light Not Working?

it makes it impossible to use the slide out keyboard in low light as i can't see the keys. i'm not good enough to know where they all are . i phoned htc uk ( milton keynes ) and they gave me a ticket # so i sent it back. got it back 2 weeks later . they told me they replaced the mother board and it was fixed. imagine my surprize when on first use the backlight kept going out. -problem not fixed. so back on the phone. they said to send it back, so another ticket # and another 2 week wait. guess what?- they replaced the mother board and guess what / it still didn't work. so back on the phone , they said to send it in and gave me a ticket # this time i insisted they replace the phone as it was the 3rd time for the same problem. i waited for a reply and after 2 days they said they will replace it in 5 days of receipt of my phone. so i sent it back. 7 days later they tell me they received it and i was to wait 5 working days for new one to arrive. guess what ?- 6 working days and nothing. i was on the phone today to them and they said that it will bee 10 working days as they needed parts for it. well i said i'm supposed to be getting a new 1 and they said they are putting it together.. what a load of bull$#!?. so i wrote them a letter.