If people want change, they'll need to find alternative avenues. (Like civil disobedience.)
Maybe this is the "Westminster Bubble" the journo's keep talking about. Whatever it is, MP's seem very reluctant to interact with their constituents unless they're campaigning for re-election. At that point they'll turn up on your door step in the middle of the day, expecting a half hour conversation.
How is a citizen meant to adovcate and voice their opinions when their representivies, and every candidate looking to replace them, refuses to engage?
This isn't really a specific question, or a critism on your point. It's just venting on my experience in recent years. Maybe someone else has had a more positive experience they'd be interested in sharing?
In any case, my sister used to work in an MP's office and even when you get auto replies they tally it, and weight it quite heavily as a representation of constituents' views (unless it's a template letter in which case it goes straight in the bin).
It definitely has more effect than signing a petition - most of them are super dumb (lower taxes!) and as far as I know not a single one has actually changed the government's position. It's just too easy to sign them and too many dumb people do it.