my mobile works but the screen is completly blank (sometimes has random lines down it)

i need to take it in to get repaired so i rang O2 and they said take it to the O2 shop, but surely i would have to take the phone to where i bought the contract from (the link), whats the phoen got to do with O2????

Phone is on contract and was told by O2 that I should have a guarentee on it but will they give me a replacement phone in the mean time?!?!?!? never had to egt one repaired before!!!

I NEED MY FOOOOOOKIN PHONE!!!!

can anyone shed some light on where to take it!??!