If it's anything like the US, I imagine your name/opinion is at least recorded by their staff. Someone who contacts their representative is more likely to vote in the next election, so "likely voter thinks X about important issue Y" is useful data.

I've written my congressperson multiple times and never gotten a personal reply, but I've heard from the staff of said congresspeople that it still counts indirectly as at least your opinion shows up in the stats they use.