What you are telling me in effect is that all the exchanges I have are ultimately disingenuous with the MP. It also tells me that the MP represents the party and not me (as they are acting as nothing more than a glorified public relations officer).
This undermines the entire point of the process and only further degrades public trust.
Here on the other side of the pond, writing our so-called Representatives to complain, produces the same kind of result. If your rep has a (D) by his or her name, you'll get back one form-letter, and if your rep has a (R) by his or her name, you'll get back the other form-letter. There's no attempt to address the points you might bring up. You write--and they respond back with their pre-baked talking points.
A politician is like ROM: Once it's written, that's it, you have to swap it out with a different ROM if you want even one of its lines of programming changed.
What you describe is the representative democratic system. Misunderstanding is the source of any distrust. It is frustrating to write to an MP only to be given boilerplate in return. But setting your expectations and continuing to advocate for your point of views is the only way to participate. One letter won't change anything, and how could it? There are other people writing opposing points of view. It's taken in the aggregate.
This undermines the entire point of the process and only further degrades public trust.