Don't "write". Modern politicians don't open paper letters and they delete emails even more quickly. Tweet. Scream on Facebook. Most importantly: get the support of social media celebs. Between elections, any photogenic teenager with a thousand twitter followers has more political power than a thousand grandmothers writing letters. If you can, get some Hollywood celebs. A visit from an attractive movie star is better than years of campaigns and lawyers.
This is the sorry state of the world in which we now live but we can only act within the world we are given.