You're Sneaky O2

When signing up I was apparently unnecessarily asked for a £100 bond. This was to be repaid to me after 3 months. Now I find that instead of repaying the bond, you're keeping my money and just debiting what I owe every month. This appears a dishonest thing to do. It enables you to keep my money for a whole year, without grounds. Please take this opportunity to defend your actions, following which I will decide whether to take the matter further. Yours sincerely, I Cook