I want correct my birth date

Hello Mod,

5 years ago I made a contract with O2. But the guy at o2 shop had put a wrong birthdate of mine in the contract.

I asked him once to change it, he took my passport copy but the date of birth never updated.

I want to know, How can I do this? Except sending it to O2 via post or FAX. I have sent the letter to o2 via post but still the birthdate is remained incorrect.

Waiting for reply,

cricketsamya