I like to think of myself as a reasonable person.
Dear Sir or Madam in what is laughably referred to as 'customer service': Thank you very much for your demand that I pay a large sum plus a fine "at my earliest convenience" -- which I have ripped into a gazillion tiny pieces. I have searched my soul at length to determine whether it was indeed my fault that your connecting train ran twenty minutes late (thus making me miss my train to London) and decided that it almost certainly was not.
I suppose the demand for payment of an additional £129, for "travelling without a ticket" on a later, slower, more crowded train (plus £20 for "administrative fees") showed pluck on your part, but did not inspire me to hand over my credit card along with my perfectly valid full-fare through-ticket for the earlier train.
Please do not misinterpret my reasonable tone. If you contact me again, unless it is to offer an apology for your unwelcome harassment, or to offer compensation for my ruined day and subsequent mental suffering, I shall hire the most expensive firm of lawyers I can find and run myself, my heirs, and -- of course -- you, into bankruptcy in an attempt to further clarify my position.
From now on, I intend to eschew your service and travel by alternative means, and will encourage my numerous friends and family to do the same.
Yours extremely sincerely,