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?
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?
This is also politics. You don't wait until last second to file a complaint. Politics is a slow moving process, not a single event, and creating support takes work over time. MEP are not subject experts so they will usually seek input long before it comes down to voting, which occur in parallel with the work of the commission.
"thanks, I can do nothing for now, but I'll keep that in mind if and when I have to vote on it"? is basically all that an citizens can expect by talking to a politician which only job is to vote on things. The same goes the other way around. If a politician today speaks about a political subject, I as a citizen can only say "thanks, I can do nothing for now, but I'll keep that in mind when its time to vote".
I never understood this argument. The comission's job is to write the laws, the parliment's job is to make sure they acceptable to all member states and either pass them or send them back.
It's the same how say, UK government uses various comissions to write legislation which then goes in front of the parliment which then either passes it or don't - and I don't think we would call the British system undemocratic(well, other than the monarchy and the house of lords - but the way the parliment works is deeply democratic). I don't believe any EU member state directly elects their law writers and comissions that propose them - the democratic part is always at the top.
But by volume most of these bills are shit and so just quietly die in a vote nobody noticed, and so most law that we actually have was indeed drafted by a special commission and put forward by the executive before it was approved by parliament.