A two page letter of complaint is far too long...
Brief, factual and very tight content that fits a binary response is what you need.
Two pages is fairly standard when the header (address areas, date, subject line, date, etc) and an opening sentence describing the core subject of what the complaint is about take up half a page, together with the final paragraph of the usual "
Thank you for your time and I look forward to hearing from you soon." plus space for signatures, etc, take up another quarter of a page. You'd do well to fit the rest onto a quarter of a page, containing even the most brief details of the matter you are complaining about.
Also remember that it is not a bog-standard letter of complaint when Transport Focus become involved. You are escalating the matter due to unsatisfactory progress so far, so additional details need to be included as to what progress has been made so far, etc.
That is assuming that you use a standard 12-point font and 1.25-inch margins. Perhaps you use a smaller font and/or ignore all parts of a letter which I consider essential for a professional presentation as detailed above. If I were to leave all those out and go for a 10-point font with half-inch margins, I probably can fit everything on one page too, but they are unlikely to be easy on the eye.