The commissioners are not elected by the citizens of their respective countries. Instead, they are selected via a parliamentary vetting process, and approved by the European Parliament.
The commission has no direct responsibility towards the citizens in EU. It is also the European Parliament that scrutinized and votes on the laws created by the commission. The commission job is only to write proposal for laws.
This is a bit like complaining that people have objections about a politician speech and send emails to the politician rather than the employed person who wrote it. Should citizens direct their messages and complaints to speech writes?
This does not seem a fitting metaphor: you complain only after the politician has read that speech. But this whole campaign is about a speech that has not been written yet, i.e., a proposal that has not been finalized. You are writing to a MEP about a certain draft that is still being worked on, and that they might have to vote on in the future.
What do you expect them to answer, other than "thanks, I can do nothing for now, but I'll keep that in mind if and when I have to vote on it"? Why not wait and write to them when they actually have to vote on this proposal?