How do i put credit on my huawei G7002? (Keypad)?

I have a new crappyy phone and i dont know how to put credit on it, I will ring the o2 credit top up line and it will tell me to put in numbers to choose a method of topping up, i need to get the keypad with the numbers on it so i can type the voucher number....How in hell do i find the keypad?