Billed for zero usage on Metronet PAYGo Option 1

[#1]

For the month 19-10-07 to 18-11-07 I was billed £ 12.73 plus VAT = £ 14.96 without any mention of extra usage. I'm on Metronet PAYGo Option 1.
Strange, as there was no usage during that period (no usage 13 Oct - 14 Dec).
Could you please look into it for me?

[#2]

Hi Mikko,
Please see the ticket on your account, thanks.
Apologies for the hassle,