As you may know, Virgin Media charge an extra £5 a month to customers who don't pay by Direct Debit.
They called me up today as my bill was overdue, and I said I'd like to pay the full amount and set up DD for future bills so I wouldn't get charged the extra £5 a month.
To my surprise they told me that because I was setting up DD, I would get a £20 discount off my existing bill - they deducted it right away, I paid the reduced amount and set up the direct debit!
I asked for the department's phone number, they gave me 0870 902 0563... but the call from them came up on my phone as 0141 300 0225 (which is the same as last month when my bill was overdue).
Worth a try if you are a Virgin Media customer :)